The problem is two fold. The first problem was that Sony did not establish a hardcore demographic of significant strength through their initial advertising campaign. Nor have they made a overarching effort to do so. Without the educated gamer demographic comprising a significant cross section of their user base it is incumbent upon them to force feed the education. Which leads to the second problem which is failing to deliver gravitas, or creating an environment of heavy interest.
When a massive cross section of your user base is ignorant you have to overwhelm their senses. Not just with great graphics, but with personality. With a strong presence so that they understand the game is good. Otherwise they are going to gravitate away from new high end properties towards the more comfortable familiar. For those highlighting a Resident Evil or a Street Fighter this explains your paradox.
The PS3 user base is predominantly core, and as such they will do as core does which is crave the established. They know what Resident Evil is. They have no clue what Killzone is, or why they should be buying it. The PS3 user base isn't more diverse it is less diverse in that it has no polar segments in its game playing demographic. Unlike the 360 which has a massive hardcore demographic, a decent core demographic, and due to its price now a significant number of soft core players. The PS3 really just does core.
Answering the next logical question what can Sony do about this. Well it is as simple as doing what Square, Konami, and other developers urged them to do early on. Focus on the gaming, and focus on perpetuating a image of being a hardcore machine. This can increase their hardcore demographic which should help their new original properties. Right now they lack the consumers with the courage to try new things.
I would suggest that Sony run itself a few Halo 3 strength campaigns. Multiple commercials that cast a wide net. Create a suitable backdrop, and highlight the games strengths with a campaign of information. Do not just show video. Create a consistent message of why gamers need to be playing this game. That is what advertising needs to do by the way. Convince people they need to have something.