Considering that many top level regiustry places are playing the game of kiting expired domains, they will all immediately attempt to register any and all expiring domains, and put them to work for 5 days testing traffic. They will then send a "oops, registered by error" so they don't have to pay for it, and then re-register it again.
This means they don't have to pay for the domains. They can keep them active for ages without issue.
Our friends over at Directnic appear to well known for this trick, one blog (
http://www.bobparsons.com/DomainKiting.html ) reporting that in March "DirectNIC registered 7.6 million names and only permanently registered — or paid for — 52.5 thousand" - less than 7/10th of 1 percent of all their "registered" domains actually stuck.
If you are playing the expired domain game at any level lower than this, you are pretty much screwed. They keep the good ones, flush the bad ones, and life goes on.
Wonderful, isn't it?