A decline in email spam?

I don't keep stats, but I also believe it's gone down. I've never used any filtering for my main address, and I know a lot of spammers have it. I now get maybe 5-10 spams a day. Instead of filtering I have this in Postfix's main.cf:

smtpd_recipient_restrictions = permit_sasl_authenticated, reject_non_fqdn_recipient, permit_sasl_authenticated, permit_mynetworks, reject_unlisted_recipient, reject_invalid_hostname, reject_non_fqdn_hostname, reject_non_fqdn_sender, reject_rbl_client zen.spamhaus.org, reject_unauth_destination, permit

Seems to work reasonably well for me.