Ditto SilverSmack. I think it isn't meant as a snub, it's just that buyers that aren't serious Etsians consider it a done deal after the item is received. I mean, I don't leave feedback for my grocery store purchases, either. For many it is simply a business transaction. In a sense, no news is good news, I'd assume.
That being said, as a seller it can be a bit disappointing. I spent two months collaborating on a custom bridal order for a client, and never got any feedback after. It would have been really cool to see a picture of my jewelry on the bridesmaids. Que sera, sera.