I want to amend my stance, as my brain went in a different direction. I don't think refs should be trying to call an "equal" amount of penalties, but they should be "equitable". For instance, if they realize they fucked up a penalty call, then I don't have an issue giving an 'even up' penalty on a marginal call. If one team gets one or two penalties in OT, you know the other team is going to be under a microscope, and the refs are more apt to not let something borderline slide.
At the end of it all, the stripes don't want to be the ones under the microscope themselves, and be seen as the deciding factor in any game.