With the number of in-game rumors there are, it seems as if they made it to where any place would be a feasible choice. In Morrowind, by the time they released Bloodmoon, they seemed to have an idea of what they were going to do. In Oblivion, they may have decided to say a little of everything to keep their options open.
Or, as a previous poster said, it's so they can make an MMORPG, so every race has a starting area. Which I would detest.