That's true. I won't argue that.So yeah, 4E is playable at level 20 or 30 and 3E often is not. But that's only because they flattened out the advancement and cut a god chunk off of each end, limiting your play options. I'm just not that impressed with it, you could accomplish the same thing for the most part in 3E by just starting at level X and slowing down the xp and treasure gains to make the game end before the PCs reach a power level you don't want them to.
I have not been in the world of D&D for a long time, but I would like to ask as this will help me better understand, is the reason some people say that games start to break down at the higher levels because optimization is possible? I have had experiences playing Diablo 2 where heavy optimization takes place and some build are definitely better than other builds and this sort of behavior is encouraged. (not a bad thing in my opinion, I like optimization. A person should rightly be concerned with getting the maximum return from his investments.) Of course I am against infinite loops and things that obviously need to be patched and I favor the way patching is done in Diablo 2 (where powergaming is possible and in fact necessary for success at the higher difficulties.), but I am not against optimization, in fact, I encourage optimization because optimization means in my view getting the maximum return from your investment.
Not really. If everyone's on an even playing field, the DM can adjust quite easily, simply by using stronger/weaker monsters at them.is the reason some people say that games start to break down at the higher levels because optimization is possible?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.