Just another consequence of the devs not knowing what they want. With one hand they make "die and retry" bosses, and on the other hand they keep all the useless "RPG" sugar-coating (equipments, stats, etc.) but they don't go well together (nobody sane would try to add RPG mechanics to Super Meat Boy)
If they wanted to be coherent, PvE would just get fixed stats like PvP, but then there would be nothing to grind. How sad...