A large database of users has value. I see that now anything like www.tinyurl.com/whatever forwards to ebay thru an affiliate link, so I'm sure that they are making quite a bit of money from what they have created.
The fact is that url shorten service consume very little bandwidth, even large directions . Some shortened url expired or cancelled, they get some traffic which they can convert to income .
Are you sure these guys made any money with YPN? Probably yeah but only 0.5% of their visitors click on the ads...