Dausuul,
I really like your post and I think it contains some great examples that could be given names so that they can be referred to in shorthand. But as the post with the archmage/keys shows, I think players (at least on the internets) can be a little too quick to call "railroading" in situations. Fundementally, it's about player choice, but a key thing to note is that sometimes other characters and the world in general are going to limit your choices. This is in itself IMO is not railroading.
So to try to be a baatezu's advocate:
DM: "Okay, you don't go on the quest to the Mountains of Mysteriousness. You're in a farming village. There's nothing to do."
Well, maybe there *is* nothing to do in the village, or forest for that matter. Just because PCs are heroes doesn't mean that every time they walk into McDonnal's for a burger they should get attacked by a dragon. I think there's a fine line between being open to the possibility of an adventure in a different locale, and feeling a mandate to provide one.
DM: "Just as you finish off the last weasel, you see another pack coming toward you. You remember that there's an enchantment on the road that keeps the dire weasels at bay."
Player: "Uhh... I guess we'd better follow the road then." <sighs>
Obviously, since you've provided some insight into the motivations of the DM, this sort of thing is pretty easy to call egregious railroading. But in a game based on what I call "fey-type" reasoning and other mythical elements, it makes sense to me that certain odd rules would apply that would encourage PCs to certain paths. A wizard very-well may have enchanted the road to keep his visiting friends from being killed by weasels. Judging these things from the other side of the DM-screen can be difficult.
Or a more reasonable example: a castle inhabited by folks that know about magic should consider the possibility that flying/teleporting enemies will attack them and take counter-measures. It's not "railroading" if the consequence of this is that an on-foot approach of the castle is the most reasonable option because an enchantment/ritual prevents other options.
DM: "It's an evil dragon. You're a paladin of Bahamut. You smite it and it dies."
Short of magical domination I can think of no caveat on this. My baatezu powers fail. The player would have to suffer the consequences of displeasing his god, and perhaps he should be given the information about Bahamut's belief's upfront, but having a god act in such a direct way is inconsistent with the rest of the game.