Ermm.. making the website name "
www.mlno.org" is free, but anyone else who wants the name badly enough can buy the domain name and then they have rights to use the mlno.org even though you already created the site with that URL name.
SMF is saying "Thanks for being loyal; here's $35 we're giving you for a custom domain name without the ".smfforfree4" part." pretty much. They get paid to have adverts, so they use that money to run the 4 servers they have, and then for those who have had SMF forums without a custom domain name, they are willing to give us one.
EDIT: Updated first post.
