Looks like Tom's feeling and logic won out over any other motives.
Now that Simontacchi's on the 15 day DL, he's going to miss another couple of starts. I think the Booker move is just the first of several, since obviously a reliever is a poor replacement for a starter. But we have 4 more games before Simontacchi's spot in the rotation comes up again, and during that time Booker is more useful than a starter sitting idle would be. It would not surprise me to see a starter called up in time for the next Simontacchi day, which would mean another move would have to be made.
And a trade could be brewing which would send Rauch and / or Cordero away in the meantime, opening the door for Lannan or Hanrahan.