Something has to be both valuable (useful) and rare in order for people to pay for it. Useful by itself is not sufficient. A piece of open-source software can't

Something has to be both valuable (useful) and rare in order for people to pay for it. Useful by itself is not sufficient. A piece of open-source software can't be considered scarce if you are allowed to make a copy for microcents. Only through legally enforced IP protections do people even pay for classic proprietary software - it's a kind of artificial scarcity (there's no moral judgement there, just an observation). But yes, hosted services and so-on are also rare (it costs more than microcents for someone else to set up an equivalent hosted service).