Well, most registrars that also run auction houses will auction off the expiring domain names. If nobody bids for them, they will get deleted. As far as I unde

Well, most registrars that also run auction houses will auction off the expiring domain names. If nobody bids for them, they will get deleted. As far as I understand it, this won't cost them anything in ICANN/Verisign fees if a domain doesn't sell as there's no renewal involved or anything. There are other registrars (usually, smaller ones) that don't auction off expiring domain names, but rather keep them for themselves. $8/year is not much to offset and if you take in consideration the occasional sale of a domain name, it becomes even less to break even. At least, this is my take on it. Some registrars (eg. EPIK) provide you with the number of WHOIS queries ran against your domain names, the IP's used etc. This is enough information to signal interest or not in a domain name. Also, once a domain expires, they can point it to their own DNS and start collecting a whole new set of valuable info.