Some providers will accespt encrypted or unencrypted communication (and scarily, the default is often unencrypted). The difference is transmission of sensitive information including credentials over an unencrypted medium (potentially over unencrypted public wifi if you use your laptop out and about).
In that case there IS a difference between webmail and more conventional pop/smtp/imap. With web browsing it is understood that if you are doing something sentive - encrypt it (using https / SSL). Unencrypted pop/smtp is often 'accepted' for smtp/pop email to your ISP on your own internet line, as the unencrypted traffic only travels over their ISPs own network (who have access to your messages and passworsd on their pop server anyway). When using a mail provider located deeper into the internet, or over media that is easier to tsap into (unencrypted wifi), then yo do need to ensure that the traffic is encrypted.
Peiraster, the original poster had a valid question.