Add me to the confused too.
All I can think of it was/is a marketing tool to say they've added X number of names, additional info, etc.
There's another similar data base that [I think] has to do with those who fought in the Revolutionary War. The name of your ancestor leads you to another "paid" database where they don't tell you the fee but say that Ancestry.com subscribers get a 50% discount if you join so you can view their data (of course they don't give you any hint what that data might be). I don't know why, but for some reason I feel this is a bit misleading to all the Acom subscribers. By listing data from another paid subscription service it's kind of double-dipping by Ancestry.com. I'm quite sure Acom gets compensated by the other company for the "leads" or the advertising.
This is a pet peeve of mine with cable TV. I pay for the cable to have something to watch 24X7 but after midnight half the channels are paid programming. So the cable company gets my money for the priviledge of watching something an advertiser also paid for.