If they do add substance to the game with DLC then I'm all for it, and its a habit they adopt then Its one I can live with for sure.
I just keep getting the niggling feeling that DLC will be something like the Theives guild quest line (probably the most fleshed out of the lot IMO) which still wasn't great. Its this niggling feeling that has me worried for the series as a whole.
I understand your "fears",but i've to say that i'm 50% confident that in the Dlcs we will see good stuff (well its no difficult improve Skyrim from this standpoint you would probably say

) the 50% is due only to the fact that after all we are not talkin' about a "real expansion" like Shivering Isles was for Oblivion,in fact the developers have said that the first Dlc could be more similar to Point Lookout in size if i'm not wrong.
But sincerely, if they gave us only the 50% of what Shivering Isles was in this first dlc i will be already satisfied.
As for consequences for your actions, how much of that was there in Morrowind, aside from "kill this character and you can't complete the main quest"? Raven Rock, which was only in the second expansion?
I think that the true landmark from which take inspiration in that regard is Fallout New Vegas ;and even Red Dead Redemption for depth of contents and story
If they add 20 more levels,new enemies,challenging dungeons/puzzles and -most of all -a good story in the Dlc i think that even the most demanding Es fans will see the whole Skyrim from a new perspective.
Who has played the Fallout games (the last two) knows well that the Dlcs could even improve the game,is that what i mean (well, ok..not all of them probably

e.g. operation anchorage) but i'm still confident that we could have good stuff for the above mentioned reasons.
Of course its a shame that the vanilla game is more oriented to "size" (the more the best ? ) than "depth" (the less but
better) but this could be even a strict choice to reach the largest number of players/people,who knows.
A wise choice judging from the success of Skyrim.