My guess is that Miami, while we beat them head to head, had a better year last year than Marshall. therefore, they appear to already have momentum sticking with a coach that was part of the success for the past few years. Marshall's record has been in a decline the last two years and we hired an outsider (i.e. wasn't already part of the staff previously) who has no head coach experience (I know neither does Montgomery but he was part of the previous staff).
I'm not saying I agree with it. Just playing Devil's Advocate as a possible justification for the .5 differential.