To start with, you're right. Digital distribution in general is volatile for consumers. While I will say that Steam, at present, is leagues better in that you must download the game purchase in order to play it (meaning, you have a direct copy of the game on your hard drive, which will remain there even if the game is removed from the Steam store), it is not outside the realm of possibility that this could change in the future.

That said, publishers having their own launchers, I'm sorry to say, has absolutely nothing to do with their fears over "the valve guy" retiring (his name is Gabe Newell, by the way), and significantly more to do with making more money. These publishers figure if they can get you, the consumer, to buy their games directly from them, they can make 100%+ of the money, instead of having to pay Steam a percentage for any transaction. Due to the limited scope of these Publisher-run launchers, purchasing a game from them is even more volatile than purchasing from Steam (at least in the current climate), in such that if the Publisher suddenly finds their launcher is not bringing in customers (which, on average, compared to the draw of Steam at present, they generally don't) publishers could simply drop their launchers and the catalog of games you, the customer, may have purchased from that launcher would go with them... again, yes, this could happen if Steam went down, but presently, pound for pound, the publisher's launchers are far more likely to fall than Steam will.

Also... for any of these services (Steam or publisher launchers), you have to download the game locally in order to run them. The games are not streaming as most movie and music content is. As such, once you install a game, you could crack them to remove any DRM attached to them (barring any game that's strictly online), then, yeah, you can self-host/store these games yourself all you want. If you buy games from GOG they make this even easier for you.