In a perfect world there is no obligation. In the world we live in, there can be. Not always, but the potential is there. Just read through these forums and people are all over the board because someone they gave a gift to did or did not do something with the gift or around the gift.
And I agree it is about the giver not the receiver.
I don't care if people want to give gifts to a therapist. I am only explaining my experience with gifts in general and that it does not enter my thinking when dealing with a therapist to want to give them anything.