2008/9: Burnett leaves as a FA. Marcum, McGowan, and Litsch all need surgery and miss all of 2009 season. That forces the Jays to basically punt 2009 on purpose, and subsequently trade Halladay at the end of the season.
2012: Hutchison, Drabek, and Morrow pretty much get hurt around the same time, forces Hutchison and Drabek to miss all of 2013, and Morrow to never be the same again (for whatever reason).
2013: Projected rotation of Dickey, Johnson, Buehrle, Morrow, Happ, and Romero. Johnson ends up getting hurt, pitching poorly, and missing most of the season. Morrow gets hurt and misses most of the season. Happ gets drilled in the head with a line drive. Romero ceases to be a Major Leaguer.
I'm not saying they are better or worse with healthy than others, but they sure as hell don't get the benefit of health that often. Last season and 2010 were really huge missed opportunities.