What general rule is this? Obviously the exclusive games mean a lot. Why else would I have bought a PS3?
There are more than 3 or 4 exclusives worth buying a PS3 for, and you're talking rubbish.
Of the PS3's top 20 best selling games,
75% are PS3 exclusives.
45% of the top 20 best selling Xbox 360 games are exclusives. Obviously the exclusives are a big deal to console owners.
There are a handful of multiplatform games that don't look as good on PS3 (Mafia for example), but for the most part the differences are negligible. I rate Burnout Paradise, Mirror's Edge and GTA 4 look better on PS3. The Crysis 2 developers have said the game looks marginally better on PS3. There will always be a few games leaning towards each console graphically.
Many people play PS3 exclusives a lot, my friends and myself included. Red Dead Redemption, Uncharted 2, LittleBigPlanet, WipEout HD, MW2 and FIFA 11 are by far the most played multiplayer games out of all my PSN and real life friends.