I've never done any true research on it, but my guess is that you're seeing too small of a sample, and any pattern you see in your neutral site games is coincidental. It's still a pretty small sample, but just glossing over some of the postseason games I see in one of my worlds shows no correlation.
Also note, that if you do look at the postseason for non-D1A, you have to remember that the higher seeds are generally listed as the home team, and therefore, it would make sense if they won a little bit more often.