I think this may be more of Ned Yost trying to motivate his guy to go out and get it done more an actual threat of sending him to the bullpen. While Capuano has certainly had some horrible outings this season, the same can be said of pretty much any of the Brewers starters.
And the 0-15 stat is a little bit misleading. He's certainly gotten rocked more than a couple of times, but he's also had some good games where he either lost or got the ND.
Jul 23: 8ip, 7h,1er, 7k - ND eventually losing
Jul 18: 7ip, 4h, 2er, 5k - ND eventually losing
Jun 02: 7ip, 3h, 2er, 10k - ND eventually losing
May 28: 7ip, 7h, 2er, 6k - L