The problem with long title reigns that go on for years is that there is only so many people you can face, and so you end up beating the same people, over and over. And then you repeat the process over and over again with new wrestlers that come up. This wasn't as big of a problem in the old days, because feuds back then (in the Hogan era) would go for several months to a year, much longer than they do now. But nowadays it is. Just look at all the people CM Punk has feuded with in the past year - Del Rio, Miz, Ziggler, Jericho, Bryan, Kane, Cena, Ryback, and soon, The Rock. Could you imagine him constantly running through the whole roster for another three years?
I personally don't want someone to keep it for four years. I have no problem with Punk's reign though, because it hasn't been ridiculously long and drawn out for me just yet.