It doesn't make sense to make dropped items disappear especially when you don't get a house right from the start, unlike in Fallout 3 which gives you a house if you go straight to megaton which isn't far.
In Oblivion you don't get your first house until you buy it for 1,000 gold. From the start of the game 1,000 gold takes a long time to get if I wasn't able to drop items and pick them up later I would be forgeted.