At first glance, Posey's stats speak for themselves.
He is hitting .334 with 22 home runs and 94 RBI. He is currently third in the National League in batting average and tied for seventh in RBI.
There are very few catchers capable of producing at such a high level, and that type of scarcity will not hurt him. There are always a lot of outfielders who produced at high levels, but such catchers are rare.
That is another reason why Posey has an advantage over his top competitors, Ryan Braun and Andrew McCutchen. Even though they are both having great seasons, they are both outfielders, so Posey has differentiation going for him.
Braun has the numbers to win this award with a .313 average, 40 home runs and 104 RBI. However, he still has the shadow of last year’s fiasco hanging over his head, and that will hurt him with the voters.
McCutchen has cooled off somewhat since his hot start and is currently hitting .340 with 29 home runs and 89 RBI. Obviously two of those numbers are better than Posey’s, but his numbers are not so much better that Posey will be at a significant disadvantage on that front.
On top of that, assuming that the playoff race doesn't change very much, Posey will be the only one out of this trio that will be in the postseason. A lot of people believe that the MVP should come from a playoff team, so for any voters who feel that way, Posey will be the only logical choice if nothing changes.
While the American League MVP race is still largely up in the air, it would be very surprising to see anyone other than Buster Posey winning the National League award.
His great performance at a historically weaker position on a playoff team should be plenty to carry him to the awards stand.