Really? My contributions to the open source world are certainly modest, but I get thank you emails perhaps once a month for applications I've released. People are quite pleasant.
Most recently I have decided that releasing open source is what I want to do, because it is what I want. I don't expect anyone to appreciate it any more.
The parser I wrote has actually made it into several linux distributions ( as well as on the distributed discs ). Several people benchmarked it and said it was amazingly fast. I'm pretty sure it is used by a fair amount of people, but since it is mainly distributed through CPAN I have no idea who really uses it or how many.
I think this is the case for what I wrote because it is a component. People in general I think appreciate tools much more than components, especially if the component is one of many somewhat inter-compatible other options. There is little love for "another thing added to the pile" even if it is different in fundamental ways.
I wonder if in part this is due to solicitation - you [by which I mean 'one', a person, not specifically you] have a "support" forum for problems, you have a note asking for contacts with bugs but generally OSS projects don't have a "comment with thanks" or a tip jar or whatever.
Guestbooks used to be the way people could offer a quick comment of thanks.
But as you say this is more likely to work for frontend user-facing projects. Stars on github or similar will show at least that people appreciate your work if they've not explicitly thanked you.
I've also had people thank me for a FOSS app, but that was also a consumer application. The fact that it was open-source was actually incidental though, I don't think anyone have actually forked or looked at the code. If they did, maybe I'd have gotten some hate mail ;)