Most Linux distributions are not well tuned, because this is too device-specific. Spending a few minutes writing custom udev rules, with the aid of powertop, can reduce heat and power usage dramatically. Another factor is Safari, which is significantly more efficient than Firefox and Chromium. To counter that, using a barebones setup with few running services can get you quite far. I can get more than 10 hours of battery from a recent ThinkPad.