I think this was the first sign of the Obama campaign's turn toward the standard Democratic, extremely risk averse general election strategy. Why not put the candidates in the same room and let the chips fall where they may? With all of McCain's confusion about his own positions does anybody really think Obama would not come out on top? Perhaps some of those McCain gaffes would actually get attention.
At the very least both candidates would have to clarify their positions, and the differences between them would become clearer to voters and supporters on both sides without the filter of the media.