To be honest I also hope the PS2 stays the best selling console and the WII won't reached it, as the PS2 ruled in every genre. WII doesn't and most likely never will.
And to say that the WII has expended the market, you're wrong, the PS2 already did with its Eye Toy games, Singstar, Guitar Hero and stuff long before the WII did.
By that logic that's like saying PS2 didn't expand the market because the NES did.
Also there were a few genres PS2 didn't rule in. Most noticeably platformers and simulation games. First Person Shooters could be argued too.
The last console to dominate all genres was the NES. (Master System had better SRPGs the SNES... in America anyway... Japan was up for grabs.)
Once again NES is greater then all using the suggested criteria.
Where does the ds fit in?
DS probably doesn't dominate racing games does it? Or Sports games i'd imagine... or 3-D platformers.
Granted... gameboy dominated all genres if your counting handhelds though.