Everyone I ride with who has disks has intermittent rubbing of pad and disk. Especially when uphill and out of the saddle. As someone who finds climbing the hardest aspect of cycling, this sound would wind me up on my bike. So they may self adjust, as you say, but do they self centre? Or is the adjusted tolerance that close that any slight flex of the wheel produces drag?
Lots of people also have intermittent rubbing of brake pads when climbing on rim braked bikes.
Have a think about how a disc brake is constructed, what the disc and caliper is connected to, and ask yourself what the likelihood is that ‘wheel flex’ will cause disc brakes to rub.