From what I've read there is a concensus that the creature re-spawn bug is caused by a problem with the Skyrim game engine. While I don't doubt that is the case, I've been experimenting lately and think that I may have pinpointed the cause to one creature in particular: sabre cats (both the reddish-brown and white-snowy type). It seems, from my testing, that all other creature seem to respawn normally.

That being said, I wanted to point out that creatures spawn at fixed locations (even though they do move around from that location if disturbed) and the type of creature that spawns (e.g. wolf, sabre cat, bear, troll, skeever, ice wraith, frostbite spider) at a given location may not be fixed depending on player level, the region in Skyrim, and other random variables. To avoid confusion: I am not talking about http://elderscrolls.wikia.com/wiki/Random_Encounters_(Skyrim) spawns such as the Old Orc. As most people know exterior wilderness areas are supposed to respawn creatures after 10 days (assuming the player does not visit that area during that time period). I've discovered that when the creature at a given location spawns as a sabre cat, killing it will permanently cause that location to never spawn any creature ever again. I've noticed that the only area which never spawns sabre cats is Falkreath Hold, which at least from my testing, never has had this bug occur. This bug tends to be especially noticable in Whiterun Hold due to the large number of fixed locations where sabre cats can spawn.

I play Skyrim on the Xbox, so if possible would someone who has the PC version and knows how to access the coding in the game that deals with respawns take a look and see if there is some difference in the way sabre cats respawn versus other creatures such as wolves or bears? I'm curious if there is there is any truth to what I explained above, which could potentially be used to fix this issue. And yes, I am aware that Skyrim development is done and that the bug will probably never be addressed officially by Bethesda.