Sure, though if you're a central provider like a registrar/ISP there are very bad things that happen no matter what you do with a domain. Since the registrar c

Sure, though if you're a central provider like a registrar/ISP there are very bad things that happen no matter what you do with a domain. Since the registrar could very easily determine whether or not the domain was in active use in the wild (and still return an error if they wanted), and didn't, I do consider it negligence. People hard-code them, they end up in configs, all over, specially in forgotten or hard-to-change places. $20 a year forever is pretty cheap for a company.