Sabathia should get the nod despite the wins, but based on the compilation of stats. #1 Santana (3.09. 15-11, 201 IP), gets passed based on him losing 5 games this year to the Indians and #2 Haren (3.11, 14-7, 202 IP) is on a non contending team.
Here's a breakdown of your considerations. I threw in Carmona who has gone completely under the radar, while having a better ERA and more innings pitched than Beckett, Verlander and Wang. BTW, he's our #2! Tribe starting pitching has sucked up a ton of innings this year and have the most quality starts among any other rotation. Sabathia's Innings Pitched is especially eye-opening compared to others. To me, these stats speak volumes in what he has meant to the team this year.
#3) Sabathia- 17-7, 3.15 ERA, 220 IP
#6) Carmona- 16-8, 3.20 ERA, 194 IP
#8) Beckett- 18-6, 3.27 ERA, 181 IP
#11) Verlander- 17-5, 3.47 ERA, 184 IP
#14) Wang- 18-6, 3.69, 180 IP
Verlander's also pitched in 2 less games than Sabathia this year.
Pitching two less, or two more games does not hold as much weight when the win column is 19 or higher.