The issue here is "age". Expired domains and Dropped domains differ by just one thing. Dropped names lose their age when they are picked back up. In todays world, most of the larger registrars send their expired domain names to auction platforms.
Godaddy -> TDNAM
Network Solutions - NameJet
ect...
Sometimes a no-name register will have a nice domain name that expired. Since they do not sell the domain in the aftermarket, the domain does actually drop and is then picked up by the faster backorder of any numbers of services.
Dropped names can be just as valuable as expired aftermarket ones - the only difference is where they come from.
Justin