I think one of the main reasons that the GM cars always come ahead on power, is because until the release of the LS1, the GM small block was almost 100% unchanged since 1955. Without any real changes in design or tooling, they were able to get a LOT of power out of an engine they released over 50 years ago. Considering how often Ford changes basic engine structure (comparatively), I see how GM stays ahead most of the time. They built something in the mid 50's that stood the test of time, and did not require any major changes until just recently. Even today, with the LS7, they are quite a bit ahead of their time, and it won't need to be changed significantly.... until the new C7R comes out that is.
That being said, GM does have it's own flaws, just as all manufacturers do. While the engine may put down some nice numbers, other factors come into play when people are buying a new car. Personally, in my past, I've always been a Chevy guy (please don't hate me, but I still regret not buying that 69 Chevelle SS 3 years ago...). I bought my mustang because it is by far the best option out there. But honestly, when the new Camaro comes out in 09, I won't rule out trading the stang for one......