Kenny seems to follow a simple formula when he builds his starting staff. He wants 4 number 2 / borderline number one starters and can live with one bargin bin veteran for the fifth starter . When the Sox decide that someone either no longer has the makings of a #2 or will never be a #2, out they go. It doesn't seem to take them very long to size someone up an the major league level. A potential #3 or 4 starter is just a guy, get what you can for him...Gone. Look at John Garland, Brandon McCarthy, Javy Vasquez, Clayton Richard, and now Daniel Hudson. I don't think he cares at all if Richard or Hudson or Ely or Aaron Poreda become serviceable mid-rotation starters, he doesn't need them.
And in theory, it makes sense. If you match up against halfway decent teams that have a starting rotation of 12345 with a rotation of 22225, you have a disadvantage in the first slot, a break even in the second slot, advantages in the 3rd and 4th slots and another break-even in the fifth. Over 10 games that figures out to be 6 wins ( slot 1 LL slot 2 WL slot 3 WW slot 4 WW slot 5 WL) .600 equals playoffs. The match-ups will be tougher against the best teams, better against the bottom feeders. At least in theory. And when you get into the playoffs, you figure one of your #2s will be hot enough to rank as a temporary #1...as Jose did in 2005. Danks looked like that guy for quite a while, Gavin looks like that guy at times - so does Jackson. If we'd gotten in, you'd figure at least one of them would be red hot...and Kenny's all number 2 staff would have a good chance in any playoff series.
I know it's not that simple and clear cut, but this seems to be the way Kenny think and I'll bet he has done this calculation.