Actually, I disagree.
I think if sales were a lot better for the PS3 relative to the X360, you'd see more companies leading on the PS3 and porting to the X360. This was true last gen and is turning out to be true this gen as well. The PS2 was relatively harder to program than the Xbox, but most developers lead on the PS2 and had inferior or equal ports on the Xbox...sounds familiar doesn't it?
You're right in that MS would still be actively seeking out publishing and marketing deals, but that is no different than any of the console manufacturers.
There is a point where because of a console sales, it reaches a kind of mass hysteria. We witness a glimpse of this every time NPD is released and not just from the hardcore.
I hardly consider the posters at Neogaf the hardcore, yet every time that NPD releases, the servers there are overwhelmed. Consumers are interested in console sales, whether it for e-penis, ego or just plain brand loyalty, they are interested.
Sony needs PS3 to sale well just like MS needs the X360 to sell well. I hope both do. Without either of them, who is going to push the tech next gen...Nintendo?