Oh you hit another favorite topic (maybe you knew that, as I do a regular recap of Badger hoops games by the analytics on one of their sites). I won't derail things too much here, only to say that KenPom and others always have a catch-all category called "luck" (or "F.U.N." on Torvik) which captures either randomness or variation that is (currently) unexplained. I think those guys are always searching for more explanatory data (and I would guess upwards of 95% of teams now use some form of PPP as a strategy from high school on up, too, so that's no longer unique).
In baseball, especially before the season starts, I just can't fathom how you'd account for something like the acquisitions of Priester and Vaughn, and their subsequent effectiveness beyond their historical performance. I just don't think there *is* data. Maybe you can give some adjuster to the Dodgers and Yankees always being able to bolster themselves, but not MKE.