Highest mr item is an ap item?

anyone find it kinda weird the item with the most mr in the game is an ap item? (banshee's veil) with 60 mr (and weirder again the build path only has 25 mr then 45 on completion) where-as the highest tank item is only 55? i know the tank items have hp as well, and 5 isnt a big difference, but it just doesnt sit right with me =P