As the driver of a high CG robot, I have a couple feelings on this issue.
We were tipped twice last weekend at the AZ West Regional, both cases resulted in a penalty. In the first case, we were playing a qualification match and a robot t-boned us in the neutral zone going full speed completely knocking us on our side in what seemed like an intentional tip due to the prolonged contact.
http://www.youtube.com/watch?v=sa-AHEtXedw&t=76m27s
This along with collisions with our robot that resulted in damage to our electronics system resulted in a red card for the team that flipped us.
In the second case, we were having defense played on us in an elimination match and were flipped over after 3 successive collisions in which we were obviously about to tip.
http://www.youtube.com/watch?v=sa-AHEtXedw&t=340m35s
This resulted in a yellow card.
Overall, my team was at partial fault for building a high CG robot. We were pretty upset, especially in the qualification match where damage was actually done to our robot. We talked to all the teams involved and they were all gracious so no hard feelings or witch hunting please. I still am adamant any play that is aimed at disabling a robot, or unintentional damage done from colliding into a robot after a tip while trying to complete objectives like breaching the defenses should carry a penalty. What kind of penalty should be awarded is something that needs to be refined in the rules. I think a yellow card is too lenient. But as a driver, I am not in favor of ending a team's regional with a red card due to the split second decision of one team member at the controls.
I wasn't at Michigan, but from the video of OP's tip, and seeing first hand what an intentional tip would look like, I would have called that a clean hit. The refs this year have a difficult job and sometimes make questionable calls, but hopefully, by champs they will have seen enough matches and examples like this thread to make fair calls.