This. TES is one of the few "pure" RPGs left and it is definitely the best. Most other RPGs are just hybrid RPGs that has some RPG aspects.
TES games are really great, probably the best game series in my opinion, but TES games aren't 'pure RPGs', Skyrim will be an action RPG at the very best. Most likely an Open World/Sandbox-Action game with RPG elements. Sure the open world/sandbox aspect gives a lot of freedom and therefor it's easy to roleplay in a TES game compared to most other games, but that doesn't necessarily make it a RPG.
In most standard shooters you have a basic choice of how to play your character (a sniper, grenade/explosion weapons guy, machine gun guy, a combination), TES games have a lot more freedom (since most of these shooters are linear) and give you more choice but the basics stay the same. You can kill people with all kinds of different weapons, ranged weapons, magic etc. but this is not much different than killing an enemy with a grenade instead of an sniper rifle.You could become archmage in Oblivion with all you magic skills being skill level 5 and never ever having cast a single spell, so the difference between a fighter and a mage was just visually.
The only real other choice you have in TES games is stealth so you sneak around enemies instead of killing them, dialogue is hardly ever an option. Speech is used to ask about things and get quests, hardly ever do you have a (meaningful) choice in dialogue other than yes/no, accept/not accept a quest.
Though it is (more or less) essential to an RPG to give you multiple ways to kill a character/monster, for it to have an actual choice (and there for allowing you to play characters that are actually different) it should have more options than just 'kill'.
The great amount of freedom of course lets players RP in the world they are given, and this is indeed what makes TES games so great but to me, RPGs should allow you to solve most challenges in actual different ways.
I certainly don't want less freedom in TES games. I used the Oblivion mages guild as an example before, I don't think it would solve anything to have Morrowind like skill requirements (well, being Archmage with 0 magic skills is stupid so maybe...) people can choose not to do the Mages Guild as a fighter, and since it's a single player game I don't care if some people don't make that choice. The way you could 'fix' the Mages Guild (not that is really 'broken or anything) is by making it impossible to complete without using magic, an example would be the Telvanni Towers in Morrowind which forced you to learn levitation. For the Thieves Guild you should have quest where detection means failure. A Ame using chameleon/invisibility and open lock instead of sneak and lock pick would also be able to do it, but I don't think most thieves guild memebers would care HOW you do it.
Well, there isn't a clear definition of RPG, so neither of us is right, but I certainly wouldn't call TES games 'pure RPGs' even though they are amongst the best games in existence.