Just so you know, my reference to it being a MBA were because it's much lighter, and thinner. Not actually referring to power or anything.
Just look at netbooks and the 11" MBA. People want the lightest, thinnest, notebook possible. I can understand why, for Facebook and YouTube, you don't need a 17" MBP. But for actual working, I'd much rather have a larger notebook than a little notebook. That's why I'm looking to step up from a 13" MBP. I thought it would be enough for everyday use, but I've found that in my engineering classes, I'm frequently having to use 6 or 7 windows at a time, and a 13" just doesn't cut it with the lower resolution. And this is freshman year, I can only see it getting more demanding later on. In hindsight, a 17" seemed too big, even a 15" seemed too big, but now that I've been using a 13" MBP for a year, I've found it was great for high school (MS Word mostly), but bad for college (Excel, Matlab, Word, Safari, etc... even some virtualization at times).