Thomas Shey
Legend
Idk, for my group we don't stop because "it's broken" but rather at that high of level it's just kind of ridiculous to play characters anywhere other than in other planes fighting planar threats (which is cool and fun and we have done it). Its the same reason Gary stopped at the low teens, not for fear that AD&D 1e didn't work, but because that was no longer considered adventuring to him and his.
As with everything in D&D, just beacuse it is there doesn't mean it makes sense for different groups and campaigns.
Over and above the issues of power creep and alpha striking (which doesn't require a lot of mini-maxing at those levels to drop into), the big problem around the low teens with 3e is that keeping track of a lot of opponents is really tedious because their specs are so busy.