An iPhone battery is about 10 bucks on Amazon (or 20 bucks if you buy "the nice one") and takes about 5 minutes to replace. In my opinion, removable batteries are highly over-rated. I used to cherish the one in my old Droid 2 because I'd have to do battery-pull-reboots all the time. With current versions of Android and iOS, however, the need to be able pull the battery at will really isn't there.
I'm sure that there are a subset of users who travel for days at a time without access to a charger, and want to carry a few spare batteries with them. For those folks, a phone with a "non removable" battery just won't work. The majority of users, however, will never touch their battery to begin with, "non removable" or not.