I'm not defending Sony. Though I am also trying to discuss the industry standard practices that they operate in. That said how come Valve lets you keep any purchased game after the license is revoked but nearly every other digital store doesn't or is hit and miss. It's clearly something in the contract/licensing deal.

In other words Sony could choose to play hard ball and only sign contracts that permit continuous use of content after purchasing it. Thereby allowing something closer to actual ownership. Though the question is whether Sony and other digital marketplaces can convince rights holders to agree to such terms in the movie/tv industry.