The world we see in the game is not the exact size, it's scaled. For example imperial city really isn't a small town populated by about a hundred npc's, it's a huge city which may have up to a million of people living there. iirc. Tamriel itself is supposed to be the size of Europe. So while the "real" Skyrim is supposed to be smaller than the "real" Cyrodiil, the game world in Skyrim will be about the same size of Oblivion according to Todd Howard.
Oh, and the game maps don't actually follow lore, I think I heard somewhere that Hammerfall is supposed to be way bigger.
Yeah, game world in Daggerfall, which took place in Hammerfall and High Rock was twice the size of Great Britain.