Here's how I think about it...
Blu-ray advantage: until Blu-ray becomes main-stream, the Blu-ray feature isn't as much of a factor as it could be. Also, by next Christmas we could be looking at a $150 standalone player. The days of PS3 enjoying price-parity with standalone Blu-ray players are over. CONCLUSION: some boost for the PS3, but steadily declining over time as standalone player prices drop.
Blockbuster game boosts: As each console's user base grows, it becomes more and more difficult to fuel big hardware boosts with blockbuster games as more people interested in those games will likely already have the console. This will be true for say, Halo 4, Gears 2, GOW2, etc. CONCLUSION: Some boost for both consoles, but declining as the bases grow.
Price-point advantage: I keep reading that the Arcade price-point isn't very relevant, because most people won't want a "crippled" console, i.e. - no hard drive. Yet those same posters say the 360 should be selling much better than it is because it's so much cheaper than the PS3. I agree with the former to some extent, although the NXE deal that will allow Arcade buyers to get a great deal on a 20 GB drive may make this less of an issue. If the Arcade is a "lame duck" version of the console, then the 360 isn't that much less expensive than the PS3. CONCLUSION: a $300 PS3 isn't going to set the world on fire, but it should provide a similar boost to the last 360 price cut.
Software libraries: both are becoming mature and fairly well rounded (with some noticeable exceptions), so I think this is no longer a factor against PS3 sales as it was in 2007. CONCLUSION: rapid gains year over year due to library maturity are over for both consoles.
OVERALL CONCLUSION: both consoles will enjoy good sales this Christmas and next year, but I don't see either doing anything spectacular saleswise unless something really unexpected occurs.
