"Bukkit doesnt sell anything". Wrong, Bukkit is a service, and the users are the customers. If you cannot support the base of those who use your product (especially while asking for donations from a 35,000+ member user base - whatever that product may be - then you need not be offering it.
I disagree.
I know you may not have actually posted this (never clicked that link, lol) or whatever, but I feel obligated to say that I disagree because there's the term called freeware and a disclaimer that usually goes with "freeware" programs.
As you probably know, a freeware program is one that is offered free; the consumer/user doesn't have to pay a cent to the whole project or author, and the program isn't a cracked/pirated/illegal version or copy. In this regard, the consumer usually has nothing to lose. However, once the consumer starts to have problems, then most will usually complain to the person/company that made it (or ask around their peers for help).
However,
some "freelance programmers" provide disclaimers on their freeware, stating that they will provide no support or online help for their freeware program. These type of programmers wish to make a program for themselves usually, and are letting others have their gift. Often, there's no strings attached to these programs ("freeware") and they wish to never help anyone who uses their program.
Long story made short, freelance programmers usually give freeware programs as a gift to the general public and sometimes (if at all) add a disclaimer showing that they will give no support to the project they're disclosing. In this case, the program can still be offered to people, but the people are thereby warned that they won't get any support from the author.