Do you think that we as players, all of us, have missed something? a cave? a person? something small but amazing?
Absolutely. I am on my fourth character in Skyrim and across all of them I have clocked nearly 400 hours and with each character I've created since the first one (which has about 190 hours) I have come across something new which I had never seen or done before be it a quest, a location, a chest or even some NPC. Even random occurrences that I had never seen before.
I am coming to believe that Skyrim is practically inexhaustible, no matter how many hours you play, much you travel or how many things you do, there is always something lurking about which you haven't seen or done before.