I don't either. A far bigger issue was the neutralization of his associations, both by a media unwilling to report on them and a Republican candidate who clearly stated there was nothing to be concerned about there, that he'd be a fine President.
You're right about McCain not getting into the issue of O's associations until very late, when he brought up William Ayers during the last debate. IIRC, Palin was a lot more aggressive about it than McCain was.