A few years ago we attended our neighbors son's wedding. We were told the reason we did not get a thank you was because the happy couple only sent them to folks whose gift "measured" up.
we once received a thank you note over 3 years AFTER the wedding-the sealed and addressed envelope was placed inside another envelope with a printed 'apology' note claiming the bride and groom upon recently moving had 'stumbled over' a box and to their 'surprise' found a number of completed thank you notes that had never been timely mailed.......... um nope-the address on the inside envelope was the same as on the one they mailed it in- which was for the home we had moved to a full 2 years after the wedding........
funny how they miraculously found them just in time to mail them a week before the invite to their upcoming baby shower arrived