Heck, there's not that much difference in side between the 15" MBP and the 13.3" MacBook. The MBP is only 1-1/3 inches wider and just over half an inch deeper than the MacBook. It's a meager 2/5 of a pound heavier (5.0 v. 5.4 pounds) and is actually .08 inches thinner.
IMHO, the 15" MBP is just as portable as the MacBook.
I know; I know
I've compared the dimensions numerous times. when you just look at the numbers, MBP doesnt seem that much bigger than the MB but when you look at the actual notebooks... the difference in size seems to be HUGE.