Not exactly true dave
[whois.us...]It's not only possible but dot.us even allows it..
Oh that. But that's only for .US domains, of course.
[answers.google.com...]
Chances are you've seen complete WhoIs templates in the Google Serps. I've seen them for my own domains and the domains of many others.
Since Google's spider records URL I'm certain there's little additional effort to extract the root domain and then perform a WhoIs look up, then store and analyze that data.
There are some ways (I've heard of but never used) to back into 'who owns what' by exploring their domain name server records. This, as you can imagine, has its limitations.