Apple used to stick 99 Wh batteries in the 15" Pros, but with the last 2 generations they downgraded that to 76Wh batteries (presumably since their battery life targets are based on Safari browsing and QuickTime playback - or at least that's all they advertise)
Yes, I'd be curious to know why they don't push the limit anymore.
But in any case, we're talking a maximum of 30% improved battery life that you can get by going bigger. Better efficiency when consuming power is likely to make a larger difference.
