This seems to be true. But seriously, how hard would it be to toggle a little marker? Honestly, if it was toggleable, I'd probably turn it off for the most part.
It wasn't toggleable in Oblivion because quest markers were used as a
substitute for directions given in dialogue. But we've heard that there will be directions given in dialogue in Skyrim, so that seems to suggest that quest markers will at least be toggleable.
Limited, or outright wrong, directions by NPCs. They're not perfect and their memories can be fuzzy.
So suppose you are given a quest to clear out some bandits from a dungeon. But you're given either wrong or vague information. If you're given wrong information, maybe you'll end up killing NPCs that are important for other reasons, and that you would have preferred to not have killed. If you're given vague information, how do you proceed from there? Do you just try to clear out all dungeons in the general area you were directed to?
There are ways around this:
1. I don't mind NPCs giving you wrong information. But I'd that like to be only when they are lying or intentionally misleading you, and I'd prefer it if there were clues that the NPC was doing this. For instance, they might have a certain agenda, and you can gather from the sort of task they have asked you to do that you are just being used as a pawn to further that agenda. So, for instance, you might get a quest to clear out some bandits from a dungeon, but the NPC you get that quest from is fairly vague on the directions. So you ask another NPC for some extra directions - but that NPC then tells you the wrong dungeon, because he/she has some enemies/rivals in the wrong dungeon. But you can kinda work that out beforehand (it shouldn't be altogether obvious, of course).
2. As for vague information, there are ways to help, but I don't see how they add a whole lot to the game - apart from the feeling of having to work harder to find stuff. For instance, suppose you are given a quest to clear out a dungeon, but the quest-giver is pretty vague on directions. So you ask a town-guard for help. The town-guard tells you where the dungeon is. I wonder, why not just cut out that middle step where you ask the guard? Why not just give the precise directions to the quest-giver? There might be a slight increase in "immersion" if you have to ask around for more precise directions, but one might also regard it as just extra tedious legwork to get to the more interesting gameplay.