Absurd discussion if you ask me, but IMHO that incident is completely different, one is a brake test trying to cause someone´s accident, while the other is a usual attempt to block someone who´s trying to pass you. I didn´t even see any abrupt change of direction, and he still left space at both sides, so I think this was more of a mistake by Coulthard who was not prepared for Alonso´s defensive move than Alonso doing something wrong.
Vettel incident OTOH is different, he brakes on a point nobody brake, without any reason as he was the leader. You can easily see that comparing Alonso´s distance with Vettel and Massa cars. I sincerely think he was trying to get Alonso out of the race.