Why can't I find any Beatles, Led Zepplin, or Rolling Stones on
itunes? Are there any other iconic musicains excluded? Who?

This may be of interest to you:

"There are no tracks from The Beatles, Led Zeppelin, AC/DC, Metallica
or Radiohead in the iTunes online catalogue (with the exception of an
album collaboration between Tony Sheridan and the Beatles, and two
Radiohead songs). Led Zeppelin and Radiohead are not included due to a
belief (by the bands) that their songs should not be available outside
of albums, while The Beatles' record company Apple Records is
currently in a legal battle with Apple Computer over the name 'Apple'.
There are, however, biographies within the Music Store for both Led
Zeppelin and The Beatles."

http://en.wikipedia.org/wiki/ITunes_Music_Store

However, the Rolling Stones are definitely on iTunes.

The Beatles and a few other artists are looking at the effect that
downloading "singles" might have on CD sales. As long as their CD
sales are still viable, or that they offer a financial advantage to
the group, I don't think you will see Beatle downloads. When you do, I
have no doubt they will be priced higher.

Thank you. I had searched wikipedia for this as well, but I went
through "the beatles" rather than "itunes." Thanks again.