It is a common, yet for me ununderstandable problem, why people think the gaming system must be actually OUT in order to get the developers to know it, in reality Resistance was under development for just as long as Gears of War was.
And while it is true that the PS 3 is most likeley the harder console to program for, sentences like "Games currently use only 20% of the true might of [place whatever console-name you want here]",are plain and simple marketing-phrases, they've been used ever since I remember and turn out to be nothing but hot air in the end (and if you want to go with those phrases, please quote Cliffy B. that says that there is alot more possible with the 360 than what was done with GoW )...
Of course I expect the PS 3 to, in time as developers get to know it's complex structure, outperform the 360 in some aspects at least (especially CPU-intensive things like Physics or A.I.), but graphicswhise we won't see alot of difference between the two Platforms (afaik the 360 GPU is quite a masterpiece), even in the future.
The reason many Games right now look and run better on the 360 is because they are Ports of latter version and ports almost always turn out to run better on the original System, especially if it is the easier to program for (we had many exeptions with PS2-->Xbox ports because the Xbox was easy to program and had quite a bit more horsepower than the PS 2, whilst the PS 3 is not all that much more powerfull than the 360).
I really tried to keep it as neutral as possible (hey, I imported a PS 3, which should arrive soon, and am already owning a 360...) as I really feel neutral about it. In the end all that decides for me is the games, especially since the graphics will be almost equal on both systems (that's maybe one of the reasons the Wii doesn't interest me one bit).
If it hadn't been for Diode-manufacturing problems the PS 3 would (should) have been out since almost a year aswell and according to Sony, developers had their SDKs already far before 360 actually launched (apparently not all that much later as MS gave out their, incomplete (alpha), SDKs..)