Re: Why does the phone permit this?
"All Android permissions should by default *not* be granted when the app isn't running in the foreground...."
I don't disagree, particularly for the camera and microphone cases you cite (though even there a user on a video call may quite reasonably want to check information in another app while on a call) but in practice Runkeeper et al. will be running in the background in a significant proportion of cases, and with the screen switched off almost universally.
The problem is whether the app tracks the user when not actively (by user action) monitoring an activity (after the user has pressed "stop" or whatever), and what is done with that information. I don't think either can easily be dealt with by Android permissions.