Moral? I'm not seeing one.

I think it's a clever way to support free and open source projects. Free edition is for everyone, trials, demos, etc. Paid enterprise version is for companies that are happy to pay to get some extra value. Build it yourself enterprise version is for people who don't want to pay, people that get less value from the product than the price, hobbyists, etc.

Caddy (a web server) used to do something similar.