I get your point, but a behemoth like Valve is so unlikely to be closing their doors in our lifetimes it's hardly worth discussing.
The real point here is that after spending thousands or tens of thousands on Steam, our next of kin or beneficiary will not get them once our lifetime ends because Steam doesn't sell games. They provide a license to access content.
Steam still suffers from the 'illusion of ownership' issue, and places that offer DRM free copies of titles are superior in this way. However it's plain for all to see that not many people care about this point. All the masses want is to play their games.
In that regard, Steam is king.