I will have to assume that is due to talents that I have when completely nekkid.
However... when I put my gear back on, my crit dropped to 17.51%. Down from 19 and change. I don't know why. Boon thinks I may have had a buff on that I wasn't aware of.
Who knows! But there you have it, by gear we need to make up about 14% critical strike to keep Vengeance up most of the time. Maybe we can reduce that by increasing our speed, so we're hitting faster so we have more crits / time rather than more crits / swing? Or whatever.
Well, I'm home now, time to play play play!
Edit: I figured it out. For some reason, my mouse-down box keeps going from melee stats to spell stats.