As always, I was there to the very end. However, comparing Broncos games to Bison games are completely different. Although I have been a Broncos fans since they late 70's/early 80's, I can't be more than just a fan. For Bison games, I'm not just a fan, but also a former student-athlete and alumni. Hence, why there is more of emotional connection with NDSU than Denver. This is probably why the atmosphere is so much different between the college and professional levels of football.
As far as the Broncos fans leaving early, I do give them crap about it. However, those leaving early (usually mid-fourth quarter) makes it easier for me to get home. Sports Authority Field at Mile High Stadium holds over 77,000 people. Combine that with an already busy interstate and any other nearby professional sports (Rockies, Avs and Nuggets) getting done (or started) at the end of the game, traffic gets horrible in Denver. Another reason why the two don't compare.