I'm really hoping fences being necessary will be gone entirely in Skyrim. It made no sense that a merchant would ever be able to tell a stolen iron short sword from an owned one. Things of extremely high value should depend on how famous/rich your character is, as a poor unknown wanderer with extremely valuable items might raise suspicion (some of the time), and unique items that were known to belong to certain people or factions should be harder to get gold for as well.
Part of the benefit of fences in Oblivion is not so much immersive realism, but as a practical way to prevent you from stealing everyone blind and immediately becoming rich at a very low level.
I think in general the item purchase prices in Oblivion were far too low and resell prices far too high, even for non-stolen items, making it far too easy to become rich.
Hopefully the fencing and general pricing system will be completely revamped, but I assume that I will still need to install some sort of mod to make all the prices much more expensive (and resell prices very low).
I imagine the devs will want to make the game more accessible to some casual gamers who would have a really difficult time if everything was very expensive. When you become too rich too easily the game becomes much less challenging and less fun IMO.