Very interesting comparison chart. Well done. My only beef is that I think the 5.5 hours of use off a battery charge is kind of a fantasy. In real world use I would expect much less time. My G4 17 inch Powerbook can't even play a movie from beginning to end without needing a battery swap and I doubt that power management or battery life has improved all that much since I bought it.
Battery life is like gas mileage -- not absolutely realistic but good for comparison. The normal benchmarks count the fact that for most average use a computer is waiting for the user, so the processor can go into a low-power state (and CoreDuo has excellent low-power management). Running video takes a lot of constant processing power and disk access, so it drains the battery very fast.
Having a lot of RAM on your machine for cache vastly increase your battery life. In fact, there's a Windows program out there that caches DVD playing to improve battery life.
BTW, for this comparison, Apple's standard battery has more watt/hours than Dell's standard, but less than Dell's $79 upgrade battery.
Another plus forgotten for Apple: Its CD/DVD drive is slot-loading.
I'm not sure about the 17" models, but my 12" iBook gets simply amazing battery life. Four and a half hours, on average, under real-world use conditions.
By comparison, my HP PC notebook gets about two hours if I'm lucky.