That's only for retail games. Some games sold on other digital distribution sites do register on Steam, like GameStop's past Fallout 3 GOTY that did successfully register on Steam, although it isn't on the retail list, only Fallout: NV is. So, that list isn't always reliable. My advice is to contact support, as you can't be sure of it unless someone vouches for it or if it is said explicitly on the site itself. Hope this helps.