But in reality its actually less since Mountains aren't things you can just walk over/on and wander.
Not necessarily, you may be able to climb mountains, granted, you're not going to just walk up those sheer cliffs we've seen, but there might be paths leading to the top.
But back to the matter at hand, we've just been told that there are five major cities, we can probably expect to see many more towns and villages, I'd assume, and I'm hoping those will be somewhat larger than their equivalents in Oblivion, I hope in Skyrim, a town or village is more along the lines of Maar Gan or Seyda-Neen or at least Khuul or Ald Velothy in Morrowind, rather than the two houses and an inn setup we'd often see in Oblivion.