There has been a lot of talk on how to attract qualified people from different fields to MO. The only consensus so far is that we need good questions in these fields in order to attract researchers to answer them. While what you describe in your last paragraph sounds reasonable at first sight, a better approach would be to post the question on MO and then email your colleagues with a link to the MO question. That colleague will become aware that MO is a place where you can ask numerical analysis questions and will hopefully consider joining the MO community, adding one more numerical analyst to the flock. There are side benefits too, such as the fact that MO is much better at rendering math than plain email.

Thus for a software question I'd want to see some evidence that MO really was the right place, that there was something special that only a mathematician could be expected to know, and not just a convenient place. In particular, to lift a sentence from Neil's last comment:

Without actually knowing the answer to the question, it is hard to be sure about it.

For a question that isn't obviously on-topic, the onus on the questioner is to make it obvious to the average MO user that it is on-topic for this site. So this sentence of Neil's sums up why I voted to close that particular question and suggested an alternative avenue for an answer.

Still, I did not (yet) vote to close this one, mainly due to the "Or, can you give me some suggestions?" [making it a general question] and the fact that the questioner might clarify in view of fabee's answer.

And, regarding Andrew's comment: the questioner seems to mainly ask for a replacement/addition of one matlab tool by another matlab tool. I used matlab the last time more than a decade ago and never used it seriously, but still I am quite sure, and a quick google search seems to confirm this, that there are plenty of places on the web were nothing but matlab is discussed. So, it seems simply wiser to ask there. So, Andrew's comment seems like good advice.

Finally (this is not meant as critical as it might sound): to some extent I find this discussion difficult, because for both questions there is at least one reason other than it being about a specific software that in my opinion definitely would warrant a closure. Is there any good or at least reasonable question that got closed just because it was about specific software?

Added after seeing Ryan's comment: to me this cetainly seems like a good question (and it seems also nobody wanted to close it). But, as Ryan says, it is not a usage question, but in spirit a question on an algorithm. And, say, if somebody asks an advanced question on symbolic integeration and frames the questions along the lines the lines of the implemantion of some algorithm in some program, then I think this person will not be faced with much problems either. Since such questions are not only about using a specific software.

http://mathoverflow.net/questions/4918/can-you-fool-snappea

Technically, it's about the algorithms that SnapPea use so it's not a strict usage question.

Interestingly, math.stackexchange DOES allow questions about software that mathematicians use.

I do tend to post a comment suggesting to the users the appropriate forum or mailing-list, especially for big-budget software like Mathematica, for the reason that they are likely to get more prompt and better help there than from the Math.SE community.

Ideally we should have some statement about software questions in our FAQ. However, I've been under the impression that "tools of the trade" questions are okay, especially as CW. For example, of all the questions I've asked on MO, this one received the most votes. So a proper phrasing in the FAQ will be a bit delicate.

Or in other words, it is not really about a specific software, but more general; Mathematica could be replaced by (certain) other CAS, and the question would remain meaningful.

What I meant to say, in accordance with Kevin Buzzard, is merely (and I believe there are at least precedences for this) that MO is not to be used as a substitute for a support-mailinglist for whatever (math) software. Indeed, I thought about writing instead "MO is not a support-mailinglist." But this felt somehow unfriendly, and so I wrote that instead.

Now, it is true, that I can imagine questions of which one could say they are on a specific math software that I would consider as on-topic on MO. So the precise wording of the comment is not good.

But, what I think is essentially always off-topic is a question of the form: I entered [this piece of code] in software X. Why does this do A (rather than B)?

Later Addition: Rereading it seems to me I did not really address the actual question, that is why I consider such questions off-topic according to the written guidelines of MO.

First, in most cases, such question are not a research level math question (and thus by the FAQs are already outside the primary focus of MO), and they are also (in most cases) not something of the form which while not being a rlmq is still a good MO question. For example, as they tend to be very localized. (What to me for example could make a good MO question, and questions like this exists, are of the form: I am trying to solve computational problem P / am working in field F. Which software would be best suited for me / there are various different tools I known of what are pros and cons? [However, this then already is not a question on a specific software, and thus would not fall under what I wrote. And, this was also a motivation for writing the 'specific' in the first place.])

Second, there is a request in the 'how to ask page' along the lines of 'doing ones homework' before asking on MO. The question of the form I described at the end of my original post, should almost always fall short of this, as typically there are more or less obvious, and not too much more inconvenient, other places to get an answer. (In particular, if a questioner would indicate somehow why s/he is using MO for the question, the situation would be different. For example, I in principle could imagine a situtation where somebody wants to use a highly speciliazed piece of OSS math software and the original developper is unreachable for some reasons and there actually is no default place to get an answer.)

So, in summary, I think that there are various reasons why the typical question on a specific software is off-topic. And, thus why I think in general such questions are off-topic. (Though, I could imagine unusual circumstances/exceptions.)

In case nobody objects or comes up with a different point of view, I will in the future add an 'in general' to comments of the form mentioned, but otherwise follow the policy I tried to sketch above, which is the one of which I thought (perhaps wrongly) was generally accepted. (Needless to say, in case this discussion should show that this was a misconception or there is a desire to change this policy, I will follow another policy.)