In all likelihood the Astros right now see Wallace as, at best, a 2-3 year placeholder until Singleton is ready. Given that, I think it's likely that Carlos will play almost every day the rest of the year- who knows, if he winds up at .280, with 18 HR, 85-90 RBI, maybe they'll only have to eat about $15- of the $18-mil he's owed next year to trade him.
So in that sense, it's kind of like cutting into Wallace's time now to ensure that Wallace and Martinez both can play full-time next year (and save the team a few million bucks too). I mean, especially with a new FO likely taking over, there's almost no way Lee is on the team in 2012, right?