LGP's download service is not being offered directly to gamers but instead to their resellers, which they will then likely make available to the customers. The first games they will be making available under this download system are Sacred Gold, X3: Reunion, and Jets 'n' Guns.
Similarly, they will be offering game rentals through their resellers where one can purchase an access key that will allow them to play their LGP game(s) for a week or a month at a time, before the service becomes deactivated. Presumably this will be at a lower cost, but the prices have not been announced as of yet.
These two announcements were made this week by Linux Game Publishing.