I don't think it's that dumb, to be honest. Remember, the goal of every leg (except the last one) is to not finish last. In the current era of travel equalization, it doesn't matter if you're second or next-to-last - everyone ends up starting at the same position in the next country anyway.
What this means, then, is that you try to take out a strong team if you think you can do it, but make sure that what you do is an attempt to advance YOUR team to the next leg. So Will & James U-Turning Leo & Alana in Brazil wasn't a smart decision, because they were in no danger of elimination and I don't think that there was much chance that Leo & Alana were going to get eliminated.
Now the girls Yielding Leo & Alana made sense because they were the last two teams, and it made sense to try and keep whatever lead they had.
Similarly, the Mine 5 knew that the girls were behind, so using multiple Yields on them helped to ensure that they stayed there.
Incidentally, I've been trying to pay attention, and I don't think there has been one mention of DeAngelo and Gary "not needing the money", which makes me think that they've told the other teams that their winnings would go to their charities or something to that effect.