You know what? Let's just be honest. The argument for Teixeira is an argument for doing it the way it's always been done. Teixeira is just another big RBI guy on a team with a great record. If he were a Twin and Mauer were a Yankee, Teixeira would hardly be an afterthought.
Look, Teixeira's been great, but he's not even the most valuable Yankee: that would be Derek Jeter. Joe Mauer, despite missing a month, has been far and away the most valuable player in the league. That's what happens when you hit .377 with power as a catcher.
Look at it another way: Joe Mauer is the only player in the AL with an OPS over 1.000 (currently 1.071). In fact, it's nearly .100 higher than the guy in second place, Kevin Youkilis, who has a 0.988 OPS. Only nine players, Mauer included, have an OPS over .900. Again, Joe Mauer is a catcher.
The only way for Mauer to not be the MVP at this point (remember, anything can happen in the next month and a half), is if you believe that an MVP should come from a team in contention and that the Twins are not sufficiently in contention. Of course, you still wouldn't get to make Teixeira the MVP at that point. You'd have to find a way to get Ben Zobrist and Evan Longoria disqualified too. And, of course, then the MVP would be Jeter. Good luck getting him out of the way without disqualifying Tex at the same time.