Evolution in a flask

I read with great interest an article claiming that evolution -- specifically, the evolution of the ability of E. coli to eat citrate, something they have never been able to do before -- has been seen in the lab. This isn't my field, of course, but I had some thoughts about it... then read Carl Zimmer's article which lays everything out very clearly. This is a fascinating development... and of course is yet another slap in the face to creationists. Not that it matters: they'll never, ever admit that there's any evidence that what they're saying is so much eyewash. Why would this particular evidence in a lab under controlled conditions make them want to drop their blinders any more than the already existing nearly endless stream of evidence they are so well practiced at ignoring?