If you publish some code and go around claiming it does this and that, you are absolutely responsible for making good on those claims. Your reputation is at stake. How much you are getting paid is irrelevant. Besides, there are plenty of indirect ways to profit from making free software.
Also, there are implicit claims in every piece of software that doesn't say otherwise, namely that it is secure, won't trash your data, follows best practices, is not full of bugs, etc.
If you want to publish "as is" software, that's fine, but it should be made explicity clear to what degree you stand behind the quality of your code.
Users have no business complaining because you won't add some feature they came up with or your pre-release version isn't solid. But it is quite reasonable to complain if an open source project does not live up to its own pretenses.
That's what this whole Capistrano situation seems like to me (sadly, I didn't even think cap worked on windows). People are irate because a project is dropping support for a platform it never seemed to work well on to begin with. Have the developers ever promised windows support? I always thought their main claim was that it's a tool to automate deploying (mostly rails) apps, and I think it works well in that regard. I didn't think those promises extended to platform support as well.
As for this case.. well, Capistrano is a Ruby lib and Ruby libs tend to work on any platform Ruby does, unless otherwise specified. Plus, it used to be supported, which means people invested their time, thinking it would continue to be. It's a weak complaint but it deserves at least a little recognition.
But the attitude bothers me more than the action. Read that message again and then look at this sunshine enema: http://www.capify.org/
Can you put that site online and then claim you're not beholden to anyone? Questionable.
For what it's worth, what would bother me is if this wasn't explicitly announced and the dev just didn't feel like working on the project anymore, or if it was a core feature of the tool that was going to be ignored in the future. Now that's something to complain about, and then go do something about if it mattered that much to me.
I've personally been in a similar hellhole of a situation (who hasn't?) doing some dev work for a nonprofit where less than 5% of the users both by number and usage completely wasted my time trying to convince me I should bring back support of older browsers and platforms for absolutely no legitimate reason other than a lack of willingness to upgrade on their part, even though the nonprofit had existing volume and discounted licenses that would effectively make the software free for them. Make a lazy <5% happy by doing LOTS of extra work possibly eschewing working on features for the other >95%, and still deliver what may be a subpar experience (think windows 98 when everyone else is running Vista) while billing them for it at the same time? No thank you.
(Funnily enough, there's a competing app that is not open source or free, and they're still not doing a great job of updating the app and adding requested features for paid customers either..)
Anyway, my two cents is that people shouldn't expect donations to make the developer(s) scratch their itches. A donation is a donation. Maybe some devs and projects would be more willing to look into things for you after one, but unless they explicitly have such a policy, I wouldn't expect it to happen.