DNS resolution appears to be inconsistent across OS X for no reason I can fathom.
$ ping example PING example.co.uk (18.104.22.168): 56 data bytes 64 bytes from 22.214.171.124: icmp_seq=0 ttl=56 time=62.077 ms
$ nslookup example Server: 10.20.20.1 Address: 10.20.20.1#53 ** server can't find example: NXDOMAIN
http://example/ resolves in Firefox, yet:
$ dig example
fails. I am pointing at my router's default DNS (10.20.20.1, as above). Pointing to other DNS servers does not appear to alter the above behaviour.