I find that interesting. My experience has been quite the opposite. I have gotten a lot more offers after interviews where I have sent a thank you note. Of course, if after an interview I don't feel like the job is a good fit or someplace I want to work, I don't bother writing one. I tend to only send them after interviews where I feel things went well and it is a place that I want to work. So, that being said, it is completely possible that the note doesn't have a darn thing to do with the offer, and I would have been given one even without the note. On the flip side though, it is one more opportunity to sell myself and to get my name in front of them. It doesn't take all that long to do, and postage is cheap, so why not.
The other thing I have found is that more and more of the people I have talked with that do send a thank you note after an interview are doing it by email these days. Maybe I am just "old fashioned" or what have you, but I think that by sending a hand written note instead of an email, even if it takes a bit longer to get to it's destination, helps me to stand out a bit more as well.