Most people don't even make it to 81, they don't stick with a single toon that long. I think it's made so that people who focus on one skillset, instead of all of them, can still make it to 81/high levels without having to train skills they won't ever actually use.
It just greases the path to the Godhead.
Some Death Overlords can be level 45 as well. Specifically, the ones with Ebony Weapons exclusively.
To answer the OP, yes and no. No Common or boss enemy levels past 80. Though there are some unique bosses(General Falx, MIraak, etc) that can level up to 100+
General Falx in particular is one of the extreme rares that can level up infinitely.
Well at level 52 I have the game on legendary difficulty and still get a good challenge, I can imagine I will still get to a point where even that seems easy but it is at least a partial solution to the game being to easy.
Also play the game from the start on master difficulty really makes the game IMO, it almost forces you to role-play your character more, takes longer to level up and even bandits get the better of you till you are level 15+ and even then a bandit Chief will own you.