Mike Wuertz is streaky - that I will not deny. He goes through periods where he's very effective, and then turns into a pumpkin at a moment's notice without much reason - the problem being that he doesn't just turn into the pumpkin for a single game, but seems to stay at least partially gourdified for days at a time.
That said, he had a generally nice June, had a bit of a rough patch against Baltimore and the White Sox at the end of the month, but came back and pitched a good inning against the Giants on July 3rd. He was then shelved for a week, and waddyaknow, when he was asked to hold down the fort yesterday, he blew up. In fact, if you eyeball his gamelog from this year, it appears that he has trouble after he's been sitting for an extended spell - a not uncommon ailment among relievers.
Here's my point: It seems very much like this move is a reaction to yesterday's performance, which to my mind, should have been at least somewhat expected given the circumstances. In fact, the previous three victories gave ample opportunity to give a guy like Wuertz some much needed work, rather than continuing to use the all-too-often-used Carlos Marmol three days in a row with leads of 5, 6, and 4 runs.
The Cubs have been pretty smart this year, but there's been some stubbornness on the part of Lou when it comes to bullpen usage, and he clearly has lost any trust he might have had in Mike Wuertz, despite his being a useful, if occasionally maddening, bullpen part. This move is more about giving Lou someone he'll use with a 5-run lead instead of Marmol - essentially, appeasing an irrational unwillingness to deploy perfectly reasonable in-hand options - and that's a shame. Wuertz deserves better.