Here's my rationale for wearing gear.
Picture a belt sander. For those of you not familiar with power tools, it's one of these:
Install an 80-grit sanding belt on it -- 80 grit is more or less equivalent to pavement in roughness -- and fire it up.
The surface of the belt will be moving at about 35 or 40 mph, which is more or less the speed you're likely to be moving if you go down.
Now...
and picture this as clearly, accurately and graphically as you can... apply the running sander to the body part of your choice. You're allowed to be wearing whatever you want when you do so.
Clear enough?