Muddy, I have heard of the same reception of others who tracked down owners. Sure, most of the time it's the happy re-union stories, peppered with "thankyous" and a great "who-dunn-it mystery" ending. Yeah. But other times, it's as you describe. Persons who look at you like your from outer space, take the object, and don't even give so much as a thankyou. I know a fellow, for example, who tracked down the owner of a class ring, and somehow made contact with the person. The person said "Mail it to such & such address" (because they were across the state from each other). The md'r said "send me the postage cost, or a SASE package at least". The owner said "if you don't mail it to me, I'm calling the police, because you have my property afterall". Can you believe it??
Another time, a friend of mine was hunting the beach, and a person came up to them asking for help finding a ring. My friend stopped what he was doing, and went to the other end of the beach, and spent nearly an hour scouring the area where the ring was supposed to have been lost. Meanwhile, the person who had enlisted his help, merely had gone back to playing volleyball with his college buddies. After an hour of work, and finally finding it, my friend came to interupt their game, and show the person the ring. The guy merely snatched it out of his hands, exclaimed with glee "that's it!", and ran back to continue to his game. My friend never got a thankyou or anything, and had just spent an hour of his time searching for this guy, in an area/part of the beach he had no intention of hunting that day.
Of course, we hope those ingrate stories are the exception.