Whats the most common type of brakes on trucks?

Doesn't really surprise me. With disc and wedge brakes (the latter being a bit of an oddity anymore), you can measure the shoes with either a 32nds gauge or a tape measure.
I don't really think the brake manufacturers have enough clout to buy off politicians the way other industries in this country have, but you never know. I also read about UPS using some new type of piston brake, details of which I don't know, but those don't seem to be catching on, either.