I want to see what happens when Gabe retires. If Steam goes public, starts hiring EA management and begins to squeeze the sponge ala Unity, we will regret not challenging Steam's supremacy earlier.
Take your favorite game today. In ~20 years, you'll be lucky if you can even play it at all.
I guess luckily the backup insurance we have is Linux... but that's also a matter of how far back of a Linux install you could log into Steam with. I guess we'll see. :)