I think there are a few reasons:
1) Microsoft is paying for exclusivity where it looks like Sony isn't (as much). $50 million for exclusive GTA episodic content.
2) Microsoft and Nintendo have 20 million consoles on the market, so they are looked on as a place where a game can be more profitable (you need double the percentage of the install base to buy your game then Wii or 360 right now)
3) Some of the other key 3rd party development tools aren't fully ready yet for PS3 to make cross platform work (Fatal Inertia delayed because of issues with Unreal Engine 3). When they do PS3 will get the support too.
4) 360 has the Live stuff as their cool feature and it is successful for what it is. Nintendo has the controller on the Wii that makes it a cool feature that is successful. Sony seems to be saying they are the luxury platform which does not sell well to regular income and lower income families who want to only spend a few hundred dollars on a console, not $400 and $500.
I'm sure that Sony will do fine next year and stuff will start coming out... But this Xmas will be OK rather then exceptional for Sony.
