i just saw that virgin radio broadcasts 3 different AAC streams:
http://www.virginradio.co.uk/thestation/listen/streams.html

- "Real 10 AAC"
- "iTunes"
- "Quicktime"

basically i want to know whether they are very dumb or smart
meaning i wonder whether it would be possible for simply offering one .mp4 stream, which will work in all players (including winamp), or not?

The iTunes stream is mp3 (same link as the other mp3 stream), dunno about the Quicktime (they use the .mov extension in the link name).
Maybe they try to make a point of showing support of many (popular) media players. The ogg stream plays nicely in foobar2000

edit: additional remark

I think that it could well be the same stream, wrapped differently in the session description.
Moreover, some of the links are identical, meaning that they are only providing different links to not confuse people about what they can use with their player.

the .mov contains an aac stream (mpeg-4 audio)