Take a look at the back of the iPhone 5. Now assuming that removable battery is a desirable feature, how would you add one without making it thicker and introduce gaps, creak, etc. It is a huge challenge with questionable benefit.
I used to have Palm phones with removable battery. The only time I ever removed the battery was to access the reset button. I did later on found a use for it: turn out there was enough of a gap between the battery and its cover to keep a folded $20 bill for emergency. The added bill also help keeps the battery cover from creaking.
I don't miss removable batteries and the compromises they entail.
Haha and I thought I was the only person who hid money under the battery cover!!!
But the industry is moving away from user replaceable batteries. It just allows them to build sleeker, smaller and lighter products.