Yes the PS3 will reach 100 million during its lifetime due to a couple of reasons
1) While Nintendo Wii is selling incredibly well I have no doubt in my mind that a good portion of it is to new gamers and thus they have really expanded the video gaming market.
2) Sony wants it to be a ten year product i don't think it will be that hard to sell ten million units a year.
I predict that by the end of the generation there will be 190 Million Wiis, 110 Million PS3's and 80 Million 360's.
Systems I own (Games)
Sega: Dreamcast (40) , Saturn (25), Genesis (50), Masters System (10), Game Gear (20)
Sony: PS1 (8), PS2 (60) , PS3 (5), PSP (12)
Atari: 2600 (18) , 7800 (10), Lynx (10)