I can see good reasons for generic batteries, too. But I got so used to the proprietary ones, too. Every camera comes with its own battery which never fits in another camera, even if you always go with the same brand (ok, some do, but mostly it won't fit).
On the other side, just taking cameras as example, proprietary batteries mostly bring more capacity in smaller packages to the table. Well, whatever. Real user replacable batteries are not my first concern if I buy a gadget. And if it really needs to be replaced, it certainly can be replaced, somehow.