Sony were the ones to trigger the most recent outcry over customer’s desire to actually own the games they buy instead of just renting them for an indeterminate amount of time.  They are not the first, Steam famously had to bring back functionality and multiplayer support to a variety of games they sold after GameSpy died, and Adobe moved Creative Suite from physical media that would work for years to an online subscription service, just to name a few.

What that means is that once an online store decides to abandon a game, not only will you not be able to buy a copy, if you thought you owned a copy already you will find that ownership didn’t mean what you thought it did.  Unless you went through GOG or somewhere similar and downloaded the full game installer, you no longer have access to that game you thought you bought.

The issue isn’t so much that you can’t buy physical media, after all the majority of your old DVD collection is probably unreadable at this point, it’s that a company can suddenly decide you can no longer legally own that game.  There are as many ways to defeat DRM as there are flavours of DRM.  You can find plenty of ways to forcibly take ownership of a game you paid for, however you are technically breaking the law by doing so.

Hackaday explains how that is the real issue.

There will be no legal way for a person to save the vast majority of their collection of games in a way that they can be installed years down the road.  In addition, sites devoted to saving old games will be in the same position and ripe for a take down notice with a possible side of lawsuit.  Without physical media or an online archive it will be as if that game never existed.  The companies aren’t losing income from a game they’ve abandoned; they made the decision to no longer sell it and in many cases the person who wants to play it already paid for it.

A company should certainly be able to decide they no longer want to provide a product, but this goes further.  They are repossessing the product they sold you and any leftover parts that could be used to rebuild the product some time in the future.