Case law is specific to jurisdiction. I don’t know where you live, and I’ve not said where I live. The way buying and selling most digital copies of games is through buying and selling licences, though some software you do pay for the download itself rather than paying for a licence. That doesn’t require case law; that’s literally just what it is, like how if I sign a contract I don’t need case law to demonstrate that what I’ve signed is a contract, it just is. Case law adjudicates matters of law which are in dispute, not figuring out whether a spade is a spade.