In reply to McBendy:
Not just helmets, why don't these guys wear neck braces?
A helmet might save you from from impact, but not from rolling over and snapping your neck. Also some sort of spinal board to protect against back slapper type falls.
Knee/elbow pads and wrist/ankle supports should obviously be worn at all times and as for not wearing a top, well an all in one suit made from a rugged fabric would be the best protection against carpet burn from the pads, I would suggest a neoprene wetsuit which would then also protect you in the event of sliding off your mat into a puddle.(of course if you're bouldering with standing water near by, you'd be a fool not to be equipped with a life jacket and arm bands)
Shockingly enough, a recent study showed that almost 1,000,000% of boulderers do not even own a pair of arm bands, let alone take them to the crag!!!!!