Not quite true. Developers have been working on PS3 devkits almost as long as developers have on 360. Remember, PS3 was originally supposed to come out early this year.
And with the PS3 coming out a year later than 360, while costing $200 more, you would think it should handily beat the 360 in graphics. But so far, the 360 is owning the PS3 in that department, in both multiplatform games as well as originals (Gears of War destroys everything out on the PS3 visually).
Many developers in the past year have said the 360 is equal to the PS3 in power, and is easier to get good results out of. The fact is, PS3 isn't better than the 360 horsepower wise. 360 is a very well designed machine, while PS3 is overly complicated, and a bit underwhelming in its design.