So basically, you want an indie developer to put their game on a system that takes royalties per purchase, thus forcing them to increase the price further, because you're too lazy to make your own backups of your game key?
That is the very epitome of laziness.
Seriously. A single notepad document containing all the keys that would be on "random scraps of paper", printed out and kept somewhere where you can find it again works fine.
Keeping the digital copy AND the paper copy is the, err, key.
You can lose the paper one, no big deal, just reprint it.
Your disk can fail, no matter, just transcribe it or scan it from the printed one.

Even better: I keep mine on both my main drive and my backup, external drive.