Battery life, in general, is really difficult to judge. Even most reviews, when done professionally, state that they get so much time, and ESTIMATE an average user should get about the whatever amount. Depending on what apps, widgets and other things you use, you could get way more or way less. Maybe you don't use wi-fi, always like having your location settings on and like your screen up full blast? Probably not going to get the same battery life as someone who uses a ton of wi-fi, no location, no Bluetooth and doesn't use a lot of widgets or emails that pull information constantly. You can go through just about every single forum for every single phone on here, read through the battery life threads and see how a few people get crappy life (either due to a bad phone or due to their settings), some get phenomenal life (luck of the draw, knowing how to use their phone, rooting or maybe using certain battery apps) and everyone else pretty much somewhere in the middle.
As the tech gets better, battery life does too, but it all depends how you use it.