Developers aren't going to create huge games for a platform that only has a 1million or so userbase. Instead they will take their hit games to other consoles like the 360 which have 10million, etc.
That means if Sony want's exclusive games (which would sell the console as you suggest), they need to get their consoles out FIRST so 3rd party developers want to spend the time to develop on it.
It's sort of like a "chicken and the egg" issue here. Microsoft overcame it by selling the 360 (and the original XBOX for that matter) at a financial loss per sale - it made it cheaper to the consumer and therefore were able to get more out into the market. In return, developers slowly slid over to Microsoft because there was money to be made by developing for the console.
Sony thought because of the success of the PS2 they could ride the developers to create all the great console games, AND charge top dollar for their consoles (and they are still taking a loss per sale!) Unfortunately their woes with Production fueled the already negative press from their marketing blunders (You'll get 2 jobs for a PS3!) and now previously "Exclusive" sony franchises are finding their way to Wii and 360. For a console who was not the "First Entrant" of this Generation, that's like a deathblow.
So you are correct in that the main issue (for all consoles, throughout history of the home console market) is getting games to drive sales of your system, the approach that Sony took crippled their ability to do so, and need to change some things before they will be able to get and sustain that type of advantage.