Per gathered info and my own calculations, the average starter ranged from a 4.45 to a 4.60 ERA between 2004-2009 in the AL, with a bit less 160 ip as the median, (for pitchers who threw more than 100 innings) so the Vasquez argument can be divided into two parts.
1) He was around average in keeping runs off the board.
2) He was very much above average in the other important part of pitching, which is throwing innings, which explains his very high WAR.
All in all, he'll be good for what the Yankees need him, but he's not good at keeping runs of the board due to his extreme long-ball tendencies.