I think E. Santana continues to have injury problems through the year. Hamels may not have a huge injury (I know he's slated to miss a start here early on), but I see him being less effective this year due to the workload increase.
When I make my rankings, I look at which younger pitchers had a large increase in workload or have had a previous serious injury. If a pitcher doesn't fall into those categories, I just pretend they'll be healthy. Otherwise, I'll go nuts predicting an injury.
...Boston papers now and then suffer a sharp flurry of arithmetic on this score; indeed, for Williams to have distributed all his hits so they did nobody else any good would constitute a feat of placement unparalleled in the annals of selfishness. -Updike