Hartley was the favoured candidate, as i understand, but wouldn't move to the Inverness area for the job, and would thus commute back and forth. It was felt that meant he wasn't committed and he would follow the others out of the club as soon as a better job offer came along. Hughes committed to staying here. That was the difference.
This time I could care less about that, and would take whoever I thought would rebuild us and get us promoted, even if not at first go. Bear in mind how difficult we have have found it in the past, and have spent significant amounts of time before finding anybody. So if Hartley was up for it (and he may not fancy it, who knows) the huge benefit would be that he could start almost immediately, and of course he knows the leagues inside out - not always the case with new managers.