This - I think - may have been better responded to by academic mathematicians rather than undergraduates.

Whether or not it's true that the only answers you'll get on math.SE are from undergraduates (and it's not), this is not the criterion for posting on MO. The criterion is, roughly, that the question has to be of research interest to research mathematicians.

Let us ignore your first post; you are right I do not know the context. I will now understand it as a pure announcement and that is fine.

Now, for the current one: on a very basic level the situation is simple. I asked you the day before not to crosspost within a period shorter than some days, and this statement had some community support. And you simply ignored this request and crossposted within three hours. Okay, you are free to do as you like. But, then I am free to be somewhat annoyed that my request is ignored. (Which is by the way a completely standard request, as documented by the fact that always essentially instantly on both or the repsective site a 'warning' appeared.) Even for a question I'd find absolutely perfect for MO I would be annoyed if it was crossposted, and would be in favor of closing it (on one of the two sites), since it is inconvenient/harmful to have a split discussion. And, I find this particullarly annoying as I cannot see a really good reason why you cannot wait some days or at least one. Within three hours not even every frequent user will have seen your question, and perhaps if seen not yet answered. You know people also have some other repsonsibilities besides answerering your questions, and might delay it the evening or something.

Then, you say the question should be answered by academic mathematicians not undergraduates. Now, while I know some undergraduates that likely could give a good answer, I would agree that a many/most undergraduate could not answer this well or at all. However, even the most superficial inspection of the math.SE user list will reveal that not only undergraduates are on math.SE but plenty of academic mathematicians; infact most of the top rep MO users have a high rep on math.SE too. And, for example, Adam Smith says on his user page he is an associated professor. So, this point is to some extent moot.

FInally, for your question. What type of deeper understanding of how/why/in what way Riemann surfaces changed mathematics do you expect? On basic grounds one would assume some basic understanding of the former and the latter is a prerequisite. Do you fulfil these? Your communication with Adam Smith suggest a clear "no", as it reveals a fundamental misunderstanding of mathematics as a field [which is fine and not unexpected for an undergraduate (in particular a non-math undergraduate)].

I suggest you follow the suggestion you got and have a look at the books that were recommended to you. If you then have some specific question the math.SE or MO (but not both at the same time!) will be happy to answer.

Anyway, good to know that you are a big supporter of MO. Here's hoping for fruitful interactions in the future.

However, yesterday we had from the OP

http://mathoverflow.net/questions/75366/primer-on-complex-analysis-and-riemann-surfaces-for-undergraduate-physics-theor

A crosspost! Where I said: "... the readership has considerable overlap. And, crosspostings are strongly discouraged; in particular when they happen in parallel. What is alright is to first ask on math.SE and then after some time (days, a week) here, taking the already obtained info into account and best linking to the other question"

Six upvotes to that, so also visibly for the OP not some unique opinion, and the OP acknowledge having read it.

Now, again a crosspost, with three hours delay. And indeed that post had an answer, which the OP did not like as it took the question a bit differently. So, the clrarified version had not time on math.SE at all. And, perhaps "days, a week" is a bit on the long side, but please at least 24 hours or a US-day.

And before that:

http://mathoverflow.net/questions/75343/semi-off-topic-tangentially-related-post-an-mo-equivalent-site-for-theoretica

On which the OP did not even follow up, the motivation is still totally unclear to me, but what is clear is that Kaveh did not appreciate it at all.

And finally

http://math.stackexchange.com/questions/64313/primer-on-complex-analysis-and-riemann-surfaces-for-undergraduate-physics-theor

the comment thread to Adam Smith's answer.

I frequently argued in favor of being welcoming and also try to live up to this, but everything has limits.

I give my thoughts in a response, I just wanted to create it quickly before the comments 'explode' further.