The battery increase for the high end i7/i9 models is to offset the increased power draw -- it supposedly won't give you much in terms of battery life in actual usage.
Or just... running stuff that kicks on the GPU? Running development tools (ios stuff, java stuff) would always kick things in to overdrive and send the fans whirring, and killing my battery. Yes, I'm often plugged in, but knowing that, if I need to be mobile, I'm going to get 2-3 hours... was a hard pill to swallow for $3700, when for 30%+ less I'd have a machine that lasted longer, had quieter keyboard, etc.
