I think it's GOOD that we would have to spend 10 minutes instead of 2 minutes on getting up a mountain.
Why?
Because the world is as small as Oblivion.
As a resident of Norway, full of mountains and probably what the devs are looking at pictures of to model terrain, I can safely say there is no mountain that doesn't take an athlete at least 8 hours to get up without a road.
Even in a game, a realistic mountain should not take 10 minutes.
Maybe the only way to get to the top of some mountains is through a long dungeon crawl full of beasts?
Maybe there are steps and a road. Should cut down the voyage a bit.
EDIT: Also, some mountains you can't get to the top of. Like http://www.nordlandturselskap.no/neted/upload/img/Torgeir_Kjus_-_Stetind_vinter_1.jpg. (Practically a stone's throw from my house)