Symbian has the world market pretty solidly, but Windows Mobile has been focusing on the U.S. market, and it's got the highest percentage there. Linux really isn't #2, not as a whole...to be honest, using that type of thinking, Symbian shouldn't either. But S60 is very VERY pervasive, so...well, it gets confusing. Anyway, AccessLinux isn't going to be compatible with Motorola's JUIX platform, etc. So it's not really a cohesive block (kind of the difference between S60 and UIQ).
PalmOS, on the other hand, is just ancient, and S60 has surpassed it in every way.