Remathilis
Legend
We might be arguing semantics a little. When I see or hear the word I go to the literary definition. "The plot of a story consists of the events that occur during the course of that story and the way in which they are presented to the reader." (Literary Devices) So It implies in my mind a lot of pre-planned structure. The vampire example (one from actual play, mind you) is just a situation with enough details so that I can respond on the fly to the players choices, from ignoring it to razing his crypt to the ground. So, yes, there is a plot, but it is in the hands of the players.
I'm arguing that when most DMs design a scenario, they usually plan out the most common course of action based on their players and their characters which usually constitute a "plot". In that regard, its a bit like a Choose-Your-Own-Adventure than a Novel; there isn't one set of linear A to B to C, but A, B, C, D, and E all exist and are pre-planned for, it is up the to PCs to decide which ones (and in what order) they will undertaken. All the elements are there, its up the PCs to provide the order and outcome of the events. They are the "reader" of the CYOA book; determining which routes the book will take to get to the ultimate goal (resolution of the hook/plot). Now of course, a CYOA is still more limited than a typical D&D game (since most CYOA writers don't have to account for, say, the reader tossing the book in the corner halfway through or the reader writing his own epilogue) but I think the analogy is close enough to work.
Rare to me would be the DM who designs plot points for all possible options (A, B1, B2, B3, etc) or only the hook (A) and makes up everything else on the fly. I'm sure both exist; I'm sure both are far more work than most people want.