Wow! I go away for 2 days from the forum and miss all this paranoia! :D
My personal opinion is this shouldn't matter. I sent a thank you note too, but did not receive any response (was a Skype interview with a second year student). This makes it the only place where I did not receive any kind of acknowledgment for it. But I do not think this has anything to do with the results, only because I think the students there are smart enough to not use this kind of tactic in the age where stuff like this can easily be discussed on the internet. It's not a very intelligent way to indirectly give results, is it?