Kos explains why he is very glad McCain didn't choose Romney:
But think, what if McCain had picked Mitt Romney as his veep choice, like so many of us were fervently hoping?
Sure, the rollout wouldn't have give McCain a fraction of the attention and excitement that Palin generated. The GOP ticket's (now evaporated) post-convention bump would've been smaller, and maybe Romney would've been less effective at revving up the fundy base.
But right now? Romney would be kicking ass. The media would treat him with deference as an economic expert, and let's be honest, he does looks straight out of central casting for the role of "serious businessman who we should defer to on the economy". McCain wouldn't have to hide him. Romney could make the media rounds, being taken seriously no matter what GOP gibberish he spouted. Rather than flail and cower, a McCain/Romney ticket would look sure-footed and confident, projecting gravitas in a time of uncertainty.