Dawnguard adds in higher level enemies, so they now scale much higher than just level 50.
Aye, true, but aren't they mostly few and far between?
I had the misfortune of fighting a wounded (and probably downscaled) falmer warmonger. By the divines, when he hit me it HURT

I dont have any characters remotely near level 81 for the record, so my first sentence is indeed speculation and nothing else. So if I'm wrong please correct me!