Why no replies to the Thank you letter

Essentially, it is a thank you card. Granted email changes things and makes stuff less formal but its a thank you card nonetheless. Would you reply to a thank you card for a wedding gift or a birthday present? No. Thank you cards are usually one way streets. Someone gives you a gift (interview in this case) you reply with a thank you card (email in this case) and its a done deal. Sure if the person replies to your email you may feel good about yourself but that is no indicator of how much they liked you, recommended you or how admissions will view your file. There are probably interviewers, out of personal protocol, that reply to every thank you email regardless of whether or not they gave a strong recommendation. In contrast, there are probably interviewers that never reply to a thank you regardless of whether or not they gave a strong recommendation.