Actually I know a Flash developer who used to use haXe instead of Macromedia (and then Adobe) tools because the language and the standard library were better, and also because the produced SWF files were lighter and executed faster. He could avoid paying for the professional Flash tools and saved a lot of money thanks to that (so he made a good donations to the haXe project). This was before ActionScript 3 and I don't know if it holds since. But the point is that it is clearly not "a language designed on indie game forums for non-programmers".
Also, I believe haXe is used for every projects of Motion-Twin[1], the company at which Nicolas Canasse works. That means a lot of good flash games which a lot of people are playing daily.
Okay, that I totally buy. Macromedia's (and Adobe's) tools were pretty abysmal.
And I guess that answers my question in general, too: It's not supposed to be a general-purpose language, and for casual games specifically multi-platform has a lot more cache.
Motion Twin, I believe, use it to power their websites - the javascript, Flash game code, server side multiplayer and web site code are all written in the same language. That's ridiculously powerful for that specific use case.
PHP wasn't an original goal; the first versions of haXe only supported Flash, JS, and NekoVM(A server-oriented VM Nicholas created). The community added the PHP target later since there was demand for using it on cheap web hosts in place of Neko.
Today there's a stronger demand for the C++ target and cross-platform graphics APIs, to get a solution that works on the web and mobile platforms equally well.
Also, I believe haXe is used for every projects of Motion-Twin[1], the company at which Nicolas Canasse works. That means a lot of good flash games which a lot of people are playing daily.
[1] http://motion-twin.com/?force=1