The difference is that YOU don't know as you are not a watch wearer. But Apple aren't holding their breath waiting for you or anyone else to say how much battery life they actually need. They probably have a Mark II that fixes the problem (and it is a problem).
My prediction is that there will not only be a newer version of this watch next year but there will be another productivity focussed watch as well which will strip out some non essentials and be a 'pro' version.
I actually love the idea of a Pro model. I'd actually prefer Apple make a Fitbit or Jawbone style bracelet that syncs constantly with my iPhone than an entire watch. I have watches that an Apple watch will never replace, so I don't need that. Give me all the health based features of the Apple watch in a good looking bracelet that Apple fully supported and designed for use with the iPhone, and I'd be a customer of that.