Their business is legit and there's nothing wrong selling subdomains. Heck, the UK goverment has been doing it for years with .co.uk.
Centralnic has been around for several years themselves. From what I know about them they provide an honest service that is what they advertise it as.
Yes, they own the actual us.com domain. They lease you a subdomain off of it, which if configured right acts exactly like any other domain would.
I would not recommend buying them for investment purposes because they expensive. But to each their own.
IMHO, companies like new.net rely more on confusing domain buyers with their "alternative" domain extension that do not function as a real domain.
If you disagree, I'd be interested in hearing why you find the practice of selling subdomains so horrible.