Steve, we use the Indirect CRL/Indirect delta CRL format to propogate revocation information for particular CAs between our VAs (Validation Authorities).
Basically, as master VA can receive information that a particular cert was revoked at a CA (even if the CA has not had time to issue a new CRL as yet). It can (and does) create a Indirect CRL with this information that it signs. The VA never acts as a CA - it never issues certs, but still needs to be responsible for creating and propogating revocation information to other VAs.
While we use these indirect CRLs to propogate information just amongst VAs, it is not a stretch to seeing clients trust these indirect CRLs for their own purposes.
Hope this helps justify why it does make sense for non-CAs to still issue CRLs.