Houston needed a right handed bat for the bench last year to compliment Erstad's left handed bat. Cheito didn't pan out and that was unfortunate because he was a switch hitter. But on occasion you need a right handed bat that can provide a little pop off the bench. Mark Loretta was a good bat, but two things about Loretta: he doesn't provide much power and he had to play a lot due to Matsui's injury, thus thinning the bench a little.
With Erstad and Blum, Houston had a need for a right handed bat and Michaels is what they settled on. I would love to see them give Carlos Lee some more days off with Erstad and Michaels on-board now.