Same here, I use that phrase too when I host a DIY grab or else, but I don't keep track of who gives what and won't hold it against anybody if they didn't bring anything.
When I go to someone's town for a service, I find it actually very helpful to know what the person would like to get as I, for one, usually tip. One time I went to an Island with a pink Cosmo only to find out arriving there that the host had their island covered in pink cosmos. I found myself a little bit ridiculous with my gift and didn't even dare plant it. Had I known what the person might have been searching for I might have brought something more appropriate.
Saying "tipping is appreciated, for example this or that" does not imply "you're a jerk if you don't tip", it is, in my opinion, a way to indicate what you could potentially appreciate should you be given a gift. I don't read it as a fee and honestly do not mind if people mention that in their thread. And I believe that most people who mention that, myself included, do not mind if guests leave without giving anything, it's ok.