After watching some interviews with Overeem, I've come to the conclusion that he knew he had a clock on Werdum, and if nothing changed in that fight until the final minute was up, he was going to win. Overeem said none of Werdum's punches had much power behind them, and they were simply thrown to try to set-up a takedown. By not committing too much to defending Werdum's weak punches, Overeem channeled more of his energy into not being baited or being taken down, and thus was able to mostly avoid the ground altogether.
Very unimpressed with Werdum. I think any strategy that relies on your opponent doing something specific, especially if that specific thing is to be an idiot, is a bad one. This is exactly what happened with Leites and Anderson Silva. Leites tried to bait Silva, and Silva was having none of it, and the end result was much of the same. It takes two to make an interesting fight. Leites and Werdum both just kept falling to their back, so it's hard for Overeem or Silva to get any momemtum going.
When Overeem fights Bigfoot, I think the fight will be drastically different. Bigfoot will stand with Overeem, and look for the clinch and takedown through that, but I also think Bigfoot will be content to strike a bit. This will let Overeem open up more and I really think Bigfoot loses by TKO. Overeem is a K1 champion, and Werdum is a mediocre striker, so overall I am inclined to give Overeem the benefit of the doubt when he says he simply knew he was in no danger with Werdum's striking, and knew he just needed to use all his energy to stay off the floor.