I'm afraid I'm one of those people whose hackles are raised when someone ends a message "Thanks in advance" but at least the poor sods who do it don't know any better. The same can't be said of the TV newsreaders, reporters and interviewers who insist on overthanking everyone they talk to. They get a guy (yes, Iain, I mean you!) into the studio to review the newspapers - not an especially onerous task, and not unpaid - and thank him as if he's agreed to say a few words after being rescued from a burning building.
Can you imagine what it would be like checking out at the supermarket if we all behaved in this way?
Assistant passes you some carrier bags.
you: "Thank you ever so much."
You hand over some money.
you: "Thank you very much indeed."
you: "Ever so kind of you. Goodbye now."
Assistant stares after you, pityingly.