Well, for one thing, those numbers for each of Mauer, Doumit, and Butera are skewed because they're not catching the same pitchers.
Butera's caught every game Liriano has started since he was promoted from the bullpen. I think Gardy keeps putting Butera behind the plate for Liriano's starts as one of those "if it ain't broke, don't fix it" things.
I think Butera has about as much to do with Liriano's recent success as the "M" logo caps do.