Well, this was unexpected.
[Edit} as a non-modder, wouldn't the new Creation Kit (or whatever) allow modders to keep up with the game?
The thing is some modders create their textures from scratch, usually the best ones are, and creating something that would look as good as what BGS is producing is not easy and takes a VERY long time.
The main thing is that we have to do it on our free time. BGS does this for a living. They have a lot more time to work on them.
EDIT: I'm not worried that there will the modding community is going to be able to keep up, I'm sure Skyrim will be just like OB in the sense that people will still play it many years after release because of it's modability. It's just that we might need to wait longer for quality mods to release.