rounser said:
I think that this in a lot of cases is one of those unspoken social contracts, like not killing other PCs in their sleep because it disrupts the game. If the DM only ever presents one plot hook, then arguably he's training the players to follow his tracks. They don't necessarily have to brush off his one and only hook to make the correct assumption about his style of play.
It's possible for such a DM to turn around and go, "Why don't you guys ever do anything apart from the obvious hook I give you", but that's unlikely, because the kind of DM who wants players to get off the tracks actually gives them a hint that those possibilities are available.
The perception of having been presented only one hook, however, is unfortunately not necessarily factual. I have been DMing for a long time, and if I've learned one thing it's that players can easily miss, forget, and ignore plot hooks.
In one session, not horribly long ago (last summer), I actually had a player suggest that they were being forced to follow one course of action if they wanted to do anything. This was because of my finally throwing a really blatant plot hook at them in the form of an NPC that wanted them to do something for him.
I responded by enumerating the plot hooks that they were aware of, or should have been aware of. I ran out of fingers. They then decided to split the party and follow up two of the plot hooks that they had hitherto ignored. Fun ensued. The obvious plot hook, which was time sensitive, went away. One day the PCs might find out what it was about, and the area that it led to has changed due to their choice not to follow it up.
(Their hooks included the obvious ones, several cave complexes, an abandoned temple, taking a boat downriver...which was what they had decided to do last session, breaking a curse on an NPC, and visiting or exploring several other locations they were aware of. Even having planned to do something specific during the last session did not prevent them from seeing it as an option during the current session. The very next session, the players conceded that they have so many options they'll never be able to follow them all. That's the way I like it.

)
What I am trying to say (in my typically long-winded way) is that an allegation of lack of choice, or a perception of having only one plot hook, is not in itself evidence of anything. Two roads lead out of town. One goes to the Dungeon of Fungal Remedies. The other goes to the Village of Restenford. The dungeon is an obvious hook, but the PCs might go exploring the other way. Or they might ask around and discover that six other possibilities open up.
When I begin a campaign, as said earlier, I like to have a strong hook for a higher-level dungeon, a strong hook for a maiden voyage, and several other possibilities for those people not interested in the first thing presented. My goal is not to overwhelm with choices. Rather, I like to allow the players to learn about the world through play and slowly add information that allows additional options. The players might start out with a strong hook to examine the Cathedral Caverns (where a local disappeared just last night...can you resuce him?), but investigation will show several other options (including other hooks for the Cathedral Caverns...can you get me a sample of green slime while you're there?). Going on that adventure opens up three more options. Each adventure after that opens up three more. Sometimes these options are loops....three adventures might hook back to the Castle of Snoring Frogs, for example. Other times they are completely new areas.
Even so, one can be accused of railroading. Perception isn't always accurate. Preception isn't enough.