Requesting WSDL Files

Here's a question that is sort of WSA-like.  I guess.  

We have some experience with WS interop, but so far it's all one
direction:  Web service on Windows server, clients on other platforms.
Sooner or later we will want to go the other direction.  One really nice
feature of the Microsoft .Net implementation of Web services is that if
you append "?WSDL" (or "?wsdl") to the URL of the Web service it will
return the WSDL file.  As far as I know this is not in any spec (I could
easily be wrong, of course), but it's clearly useful and I'm using it.
So the obvious questions are:

1 - Is this indeed part of some spec that I don't know about, so one
should expect it on other platforms?

2 - If not, have other major vendors been doing this too?  Is it by any
stretch becoming a de facto standard?

3 - If so, is there any case preference on platforms that tend to be
more case sensitive than Windows?