Fanbase of a franchise is more important than userbase of a console. After all, consoles are bought for the games, so the fanbase is more likely to opt for the console the their preferred games are coming to. That was a bit wordy, but it still makes sense. :P
Let me give you some examples:
GTA: SA sold ~15 million on a userbase of 120+ million. It was the best selling ps2 game of all time, yet it only had a 12.5% attach rate. In comparison Gears of War sold over 5 million on a console with only a 17 million unit install base. Does this make Gears more popular than GTA? Hell no. Would it have outsold GTA if it had been released on a console with a 120+ million userbase? Most likely not.
The MGS series has a large fanbase, many of which either bought a ps3 for MGS4, or are planning to buy a ps3 for MGS4.
Also, the ps2 only had a ~16 million install base when MGS2 was released.







