I see those as different things. With domain registration, someone at CCC is the registered agent for ccc.de. It seems that such a person would be ultimately responsible for what happens at, say, the jabber.ccc.de service. Yet probably the folks at Automattic don't want to take ultimate responsibility for what gets posted or (via WooCommerce plugins, sold) at foobar.wordpress.com.
Careful. There is a big legal difference between username.wordpress.com, where Automattic _is_ in fact operating the service behind that subdomain, and merely being in control of the DNS entries, with someone else operating the service behind that entry.
This reminds me of the case of a friend some years ago. He owned (owns?) a domain that is pointing to web servers operated by Wikileaks, and got sued over some illegal content on that site. The court agreed that he was not in control of the content, and that it was _not_ proportionate for him to take down the whole domain (and *all* its content, most of which is legitimate/legal). And here we're even talking about the second-level domain, not a subdomain! We can include link shorteners and (sub)domain forwarding/dyndns services in this line of thinking to make it clear that there is a legal difference.
So, you can own a domain, and not be responsible for the content of a (sub)domain. Remember, all this is evaluated on a case-by-case basis in civil law countries.
-- moritz