This was mentioned on a podcast and i agree with them. Although Syrim (and other TES) have a "main questline", there really isnt one in the game. What we do have are loads and loads of mini questlines such as the Civil War questline, Mage guild etc and these make up the game. The "main" questline is just another one of these questlines and doesnt stand out over any of the others.

I'd say the presence of dragons makes the main quest stand out slightly more.

no, there really isn't a main quest... there wasn't this whole dragonborn thing and huge massive dragon that attached Helgen...

Skyrim does of course have a main quest line but it's disappointingly short, compared to Oblivion's main quest line which was quite a bit longer and had a lot more storyline and character background behind it. Oblivion's main quest was far from the best but for this style of game it did the job, skyrim's fails on the point of view that it doesn't even seem to be the longest quest line and if not for the whole "world-eater" bit would be mainly forgettable...

I would say the lack of epic feeling to the main quest is what didn't make it stand out for me. It got stale really fast and after I killed Alduin I just sighed and said at least I get to fight Elder Dragons now and call Odvakin. That was my personal experience with it though. All my other characters besides my first I do not even bother to touch it but to get a few things unlocked.

The main quest of the game is the personal character him/herself.