The fighter on the end of such an exchange must be engaged in an "active defense". The stoppages usually come very quickly when that active defense isnt there, and the UFC gets a fair ammount of critisism for quick stoppages.
Gimme a break, that us almost as useless a reply as Shady or Kimmy. Many fighters are no longer in an "active defense" because they are already pooched. And when do they usually get pooched? When they are in an active defense. All you have said here is that once a guy is knocked out or gives up, the other guy has to stop beating on him. Nooo....
Not really. You need to win the fight. And with the rise of Brazilian Jujitsu a lot of fights are actually won by the guy on the bottom. In fact I would say that when the guy on the top is the "full guard" of the guy on the bottom that position is basically a coin toss. Silva beat Sonnen from the bottom at UFC 118, and Fedor Emelianenko was beaten from the bottom a few weeks ago as well.
So from the few examples you cite, where do you get "a lot of fights?" The fact is, delivering a downward blow to a defended head is still going to cause damage regardless of who has the advantage. And sitting on a guy, pouding away at his head is going to cause damage. Really.
Fighting on the ground is just part of the sport.
Its probably actually LESS dangerous than standing up and trading blows.
Yes, cowardly things usually are "LESS dangerous." That's why they are cowardly things.