Yep, they could have put a 99wh battery in it and gave it another ~33% battery life (the 2016 15" tbMBP has a 76wh pack while the 2015 had the 99wh pack). Given that 100wh is the largest you can easily bring on a plane, I'm sure many people would have been happier with "up to 13 hours of battery life" instead of "10" right now.