True but it just feels like a lot of mods are just fixing bugs and glitches in the vanilla game rather than sidegrades.
It is nice that they support modders though. Just wish they took some of the ideas and ran with it for the next TES game. People want more than a hack and slash. They want it to be immersive and more detailed. Hell I loved how books in morrowind were quests in and of themselves to read an entire series and how they were actually fun to read. And that was a minor thing.
Its just my opinion and I could rant about it and I imagine many others already have. So I'll just be glad they allow modders to do their work.
At least between Oblivion and Skyrim, I can guarantee you they really did look at the popular mods to correct their game. There are soooo many issues in vanilla Oblivion that don't appear in Skyrim. Such as leveling, psychic guards, leveling, sneak, leveling, merchants, persuasion (ok they simply removed the stupid minigame), leveling, combat AI... did I mention leveling ? All those issues were fixed by popular mods for Oblivion, and the TES devs sometimes very blatantly copied the modders to make Fallout 3 then Skyrim. Also, some new features of Skyrim come from mods in previous games, such as the final strike animations.
The problem is that, even with all the inspiration coming from mods, making new content such as quests is a very resource-consuming activity, you can't really expect them to improve the quantity and quality of quests unless they start generating them automatically like in daggerfall (which woud let them concentrate the work of quest writers towards the "quality quests", the program taking care of the "quantity quests".