I think I would disagree with you there. In a forest, you may not be able to do a resection, but you can calculate a bearing on your map and then walk your bearing. In a canyon, there are a lot of tricks canyoneers use. You can count the number of side canyons, checking them off on your map as you pass. You can shoot a bearing up each side canyon and check the bearing against the map. You can check off the twists and turns of the main canyon as you pass through them, marking them on your map. Again, you would verify that you're in the twist or turn that you think you are in by shooting bearings. Even in a snow storm, you can still calculate and walk a bearing.

Now, don't get me wrong, I'm not disagreeing with you overall. BobS's analogy with matches vs. a lighter is a good one. I'm merely pointing out that there are a few tricks left in the ol' map and compass bag even in the situations you point out above. Of limited utility under some conditions (whiteout), but tricks nonetheless.