Just force them to have a PIN, with a long timeout
I have a PIN (password, actually) on my phone, but it only is needed to unlock my phone if it has been four hours since I last unlocked it. So pretty much first thing in the morning, otherwise it isn't required. Since I don't leave it laying around that's the security/ease of use trade I've chosen to make.
If someone steals my phone, it will be unlocked at the time of theft (unless they break into my bedroom in the early morning) so they'll be able to get at my stuff. There isn't anything sensitive like banking info or whatever so aside from the inconvenience it wouldn't really hurt me. Even if I didn't have Apple's "activation lock" my phone would still be useless in the future because of that password - you can't clear it or reset the phone to factory defaults without entering the password, so the first time it is left laying around for 4+ hours, it becomes a brick.
Obviously thieves don't know this, so if they stole it and sold to an unsuspecting sucker quickly enough it would still be unlocked and the sucker would be the one to lose out. However, if thieves knew that all phones (well at least all newer phones / phones with updated OS) had a PIN or password required, they'd know all would have this problem. Buyers of shady phones would quickly release they're getting screwed and would not buy them, eliminating the incentive for thieves to steal them.
It isn't perfect, someone can always set a PIN of 1234 or a password of "password", but for the most part it would eliminate phone theft. Of course, activation lock would do that as well, so this solves a problem that has already been solved...
Biting the hand that feeds IT
