I think Safari does some type of domain resolution first, to see if the domain name with ".com" exists. Otherwise it requests the name as typed (perhaps in case it's a local network service?). If you try it with a domain name that exists, it should work.
Safari also seems to have a slight delay on the keyboard shortcut for some reason. That is, if you press and release control+return immediately, it may still go to a search. But if you hold control for about half a second and then press return, it should navigate to the .com.
(Chrome does not have this delay; control+return navigates to the .com immediately.)