It doesn't just support it, it requires it.
I am sure you can send email to GMail accounts with unencrypted SMTP. Just look at the incoming "Received" headers. If they do not contain a "cipher=" section, the connection was not encrypted.
I think what you mean is that GMail requires you to use https for their web interface.
gmail requires STARTTLS (or ssmtp) when an authenticated user submits outbound mail to them via SMTP (http://support.google.com/mail/bin/answer.py?hl=en&answe...), which is what he may have been mis-remembering. But, yes, it is incorrect that all mail sent to gmail.com addresses is TLS encrypted.
$ telnet smtp.gmail.com 587
Trying 173.194.67.108...
Connected to gmail-smtp-msa.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP ea6sm27303065wib.5
HELO zwp
250 mx.google.com at your service
AUTH PLAIN [elided]
530 5.7.0 Must issue a STARTTLS command first. ea6sm27303065wib.5
$ telnet smtp.gmail.com 587
Trying 173.194.67.109...
Connected to gmail-smtp-msa.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP ff2sm43397967wib.9
HELO zwp
250 mx.google.com at your service
MAIL FROM:<test@example.com>
530 5.7.0 Must issue a STARTTLS command first. ff2sm43397967wib.9[1] http://support.google.com/mail/bin/answer.py?hl=en&answe... [2] https://support.google.com/mail/bin/answer.py?hl=en&answ...