It wont matter how many games they port on that box i wont buy one, even if they make a 100% perfect arcade port of MMP.
...and this is what unwavering brand loyalty does for you.
Seriously though, there are many reasons a smaller company like Cave would not want to develop for the PS3:
1. Cost. Sony's Dev kits are a great deal more expensive than Microsoft's Dev kits. Bluray is more expensive than DVD.
2. Ease of development. The PS3 is notoriously difficult and time consuming to program for. Why Sony chose such a bizarre processor architecture is beyond me. All of this leads back to reason #1.
3. Support. Sony's track record this gen for technical support of third party devs hasn't exactly been something to cheer about.
4. Mind you, this is hearsay: Sony apparently told Cave they weren't interested in their titles.
5. This is speculation: since Sony is still selling the PS3 at a loss, there is a strong possibility that their licensing fees were also higher. Not good if you want to maximize profitability as an independent publisher/developer.
Not hating on the PS3, just sayin'.