Reportedly, Apple has double-checked battery life on real-world MacBook Pros and believes that the battery is behaving properly. The problem stems from a combination of both modern Intel processors with the very nature of battery life estimates. An operating system can only calculate battery life based on what's happening at any given moment, which is a problem when the Skylake-based chips in the new MacBook Pros have rapidly changing power states. You may be getting solid battery life in practice, but you won't see that in the estimate if the processor is running at full tilt when you're checking the menu bar.
There are other changes and fixes coming with this update. It tackles a serious graphics bug with newer MacBook Pros that triggered "visual artifacts," to start with. Also, it's clearer about what happens when you use iCloud storage syncing (which backs up your desktop and Documents folders) or Optimize Storage (removing files when backed up to iCloud) so that you're not alarmed when files seemingly disappear. You should also see improved Bluetooth audio when using FaceTime or Siri, a better Auto Unlock experience and support for new installs of Windows 7 and 8 using Boot Camp. In short: even if you're on a desktop Mac and don't care about battery life, there are quite a few reasons to update.