Actually it is. The Registrar has control of the upper layer of the WHOIS server; unless specifically redirected to the root servers, each query is performed at the registrar's servers. Some registrars like GoDaddy don't even allow full WHOIS unless it's performed directly at that upper layer. However, it seems that this applies only to Verisign-controlled TLDs: .com and .net
is it only possible if the registrar of the specific .com or .net provides this information, as the registrars operate the whois servers for .com/.net. When it comes to ccTLDs, in most cases the whois servers are operated by the registry and they normally do not provide these informations.