iserith
Magic Wordsmith
I am sadly (or happily) far from servant DM, and "no" retains its virtue at my table.
While my Table Rules are generally directed at the players and, in with respect to Rule #2 in particular players interacting with other players, a DM can also follow the tenets of "Yes, and..." under the standard adjudication process. The player describes what he or she wants to do. The DM then narrates the results. The results don't have to mean success - failure isn't the same as saying "No" to what the player attempts. It's just saying that the attempt failed.
Now, I do still engage in some "Yes, and..." with the players if in the course of their action declarations they make reference to something that has not yet been established. I play by the general idea that if it hasn't been said aloud yet, then it doesn't really exist. So at times I'll latch onto something they said and build on it, adding it to the world as if it's straight out of my prep. This is particularly true when it relates to the character's backstory.