You must be kidding. Don't tell me the company that has the best designs in the world can't come up with a door mechanism, you're simple defending Apple. That just looks silly. Its the general psychology, mind finds reasons to justify things we like.
I'm sorry your responses are just silly and unfounded. The whole "defending apple" bit is getting old. Everyone is telling you there is simply no room for a hinge mechanism, and a sliding mechanism would introduce a seam which Apple won't go for.
If your so great at battery compartment solutions please go apply to Apple as an industrial designer and show them how its done.
If you want to change your battery, go to iFixit's website, they have four pages that show you how to tear your iPhone apart if you wish.