I'll give you that Mac owners do have to deal with the frustration of not having access to some specialized software that would be very nice to have.
Here is a list: Keyhole from Google, WorldWind from NASA, some stock quote streaming software, lots of games (this isn't a problem for me as I am not a gamer), and I suppose there are lots more.
Yeah... BUT...
A lot of that FSF/GNU Software (GPL'd stuff) could be ported by smart programmers with OS X knowledge. They've got nearly everything written for free already, other things are under development.