Meh, unfortunately the most important smart phone app is the web browser, and what the browser has to do is dictated mostly by site operators, and web sites have an expansionist hunger for more and more cpu power and screen space. So phones have to keep getting bigger batteries even as the electronics get more efficient, because the work loads get heavier faster than the electronics can keep up with. Once you have such a big battery, you may as well also have a big screen, especially since you need it anyway to keep the web sites readable without a magnifying glass.
It is a vicious circle. I blame the rise of non-removable batteries and the transformation of javascript from a scripting extension into a full fat application framework. It would be great if more sites had public API's.