There's real scarcity. There are only so many five letter words with a strong relevance to the internet, and only so many tlds. Only one entity can control example.org at a time, so there you go.

Would I pay for a premium domain name? Probably not. They might make sense for some uses though. I'd rather them be available at a public price than through someone who bought as many five letter words as they could and then sells them privately.