They still don't want to make a point of it. Niggling about the small stuff is something you do when you're down, if then.
Political jujitsu has been employed heavily in the past two months, as "spread the wealth around" and "the fundamentals of our economy are strong" have made their rounds. They worked because they were tied into broader themes, such as the opponent being a socialist or out of touch.
In this case, the busing can be tied into multiple instances of condemnation while being just as guilty. Romo's post on the college professor falls into the same narrative, a narrative that was open and available (see also: multiple instances of outright lying) but rarely used.
Naturally, it's not to be a cornerstone of the campaign. This was McCain's mistake. However, if balanced with the message, then it's a perfectly effective tool.