A large majority of my friends are huge MGS fans, none of which have a PS3 yet (including me).
When MGS3 came out, me and 5 of my friends got it day 1, we were all convieniently 'sick' and had to miss a week of college.
Games much more enjoyable, when you know you friends are playing them at the same time. it becomes a sort of 'race' to finish the game.
I am personally waiting to get a PS3 in the hope they re-introduce BC in the EU. However, no BC PS3 at MGS4 launch= i don't care, i will buy a PS3 anyway, and i know most of my friends will too.