The nice thing about steam is that:
1: They're established, I don't have to worry about my CC security
2: I can re-download forever* on any computer. It is impossible to overstate how big of a deal this is.
3: Nothing to remember. No serials/keys to keep track of. No installers to back-up. IT JUST WORKS.
4: Auto-updates
2. itch.io provides the same mechanism. You are paying for the game, not the single download.
3. As long as you can re-download the game, then there is no reason to save the installer. Serials/keys are up to the discretion of the game developer and I don't see why giving the game developers control is a bad thing. I think most indie games are against DRM anyway.
4. In order to support auto-updates, the game developer has to invest in the Steam APIs. There is nothing stopping games on itch.io to using out-of-band updates.
For 2 & 3, that's great, but to be honest there is a huge burden of proof - frankly, I don't really expect any random startup that doesn't even have a .com domain to be around in 5 years.
1: I like not having to launch Steam to play my games.
2: I know there are good games that exist that aren't on Steam and am more than willing to go through a CC form or PayPal.
3: I'm slowly getting irrated with games with DRM, online-only, DLC.
I think itch.io is a win for these niches of indie game developers and consumers who buy indie games.