Verlander is a power-pitcher, who relies on an incredible fastball that has all sorts of crazy motion to it. Maybe there was some talk in the Detroit Management about whether signing that kind of arm to a long-term deal was such a great idea. But he's all of 26 years old--he'll finishing up that contract right about the time his arm is just beginning to slow down.
And consider--the Yankees spent more not only on CC Sabathia (not to mention an extra 2 years on the length of the contract) who is "husky" and also two years older. The Yankees also spent more to get AJ Burnett, who is 7 years older than Verlander, and who's best years statistically compare to Verlander's 2009, but are further in the past.
As a Twins fan, I'm unhappy that Verlander is still in the AL Central, but it is hard to argue against the wisdom of the deal from either Detroit's or Verlander's perspective.