I just realized what it is I have a serious problem with when it comes to upsets in HD.
If there's an upset because the underdog played out of their minds -- perfect game plan, going nuts from beyond the arc, something like that -- I don't really have a problem with it. And pretty much every "ridiculous" real life upset that gets cited follows that script, from 'Nova over Georgetown on up.
On the other hand, if there's an upset because the favorite plays way, way, way below their capabilities, that seems very wrong to me. The game that stuck in my craw (and hastened my exit out of HD) was one in which my very solid Naismith Tennessee team shot something like .136 from the floor against a defensively-mediocre-at-best sim-coached team.
Now, from a standard deviation perspective, both results are probably equally likely. From a "narrative" perspective, though, the first scenario makes sense while the second one doesn't.
Upsets happen because a heavy underdog does absolutely everything right.
Upsets don't happen because a heavy favorite does absolutely everything wrong. Teams that are capable of doing absolutely everything wrong wouldn't become heavy favorites in the first place.