Well, first off, I corrected the Morrowind-Oblivion mix up a while before you even posted this.
Second, you can tell that all games since Daggerfall have aspired to be Action RPG's based on the core combat mechanics alone. Real-time (Non turnbased) Is the cornerstone of the wall that breaks RPG from Action RPG. (As all true-blood RPG's are based on the DnD turn based system, perhaps modified in some way like FF's ATB). As technology has reached the point where collision and hit calculations can be matched appropriately, with less strain on hardware, action RPG designers have been able to put more focus into the combat.
Also, Morrowind was scaled, all Bethesda's games have been scaled. Spend a little time in the construction set and you can see that. What type of monster that spawns is dependent on what level the player is. To be quite frank, the enemy scaling in Skyrim is almost identical to Morrowind in every way, the chief exception being NPCs (Named).
First off, I would like to say that I've probably spent more time in the Morrowind construction set than you have, and I know how Morrowind is built. I said, "Morrowind was not fully scaled by any stretch of the imagination." Some loot was random (keyword, not scaled), some creatures wouldn't spawn until you were around level 4-5 or so, and the higher level you got, the more cliffracers would spawn, but minor things like that are about the extent. If YOU had spent time in the construction set, YOU would know that everything in the game was hand-placed, and nearly everything has a static level. There are even some NPCs that appear to be unnamed that are in fact unique (or semi-unique), in the case of the NPC, 'http://www.uesp.net/wiki/Morrowind:Vampire.' You won't be able to walk into Dagoth Ur (the citadel) at level one and go on a killing spree (you'll likely die on the way up, or on your first encounter inside). You won't be able to walk into any tomb you want without getting killed in a few hits. MOST of the game is static and nonleveled.
Now you're speaking as if you work for Bethesda and know what their design plans were from the beginning. Many other games around the time frame were action-RPG-esque titles with good combat systems (Skyrim and Oblivion have rather lacking ones, unless you find SWING SWING SWING until it's dead to be fun - and while I admit that Morrowinds was infamously the same, at least the skills and attributes of your character were fully taken into play and you couldn't just rambo everywhere). To be an RPG, a game does not need to have turn-based combat. There have been several RPGs that provided seemingly both, but the second you engaged in combat, it became pure dice-roll awesomeness (KOTOR), and there have been some games where it's up to the player to execute his 'turn,' in the time provided to him. I would cite Morrowind as an example. You can move around (won't really help much), you can not attack (won't help you at all), you can not do anything (again, not helpful), you can attack slowly (no clue why you would, but you can - and to elaborate, I mean just taking a lot of time between swings, not holding your swing to make it more powerful), you can attack at full speed (not holding your swings back), or you can attack at full speed (holding your swings back, slower), or anything in between. Still, everything you do is controlled by a dice roll. The only thing that isn't controlled by a dice roll is your ability to activate unlocked containers/doors, and to move on a 3d plane. I wasn't talking about 'true-to-the-roots,' like 2nd edition DnD, but I would say Morrowind even still is very true to RPG roots, in that nearly everything is a dice roll and it still kept it fresh and on a modern medium.
What does any of this have to do with the suggested level requirements of the Dawnguard DLC?
Like I said in the reply, absolutely nothing. I don't know why you would ask me what its purpose was when in the quote I dropped the subject saying it had no purpose.
By the way, how all of this relates to the DLC is that Bethesda have had a similar strategy of how they handled DLC, even back during the time of Morrowind's prime whenever it was less expected to cater to everyone. There is no way, now, that this DLC won't cater to everyone in some way.