We're planning to do both of these but... not til next year. Sadly I can't give you future stats XD
I'd say it's not a bad thing to put out a paid game on itch, because you don't lose anything other than potential views of people who'd only play for free. And having a demo on your page fixes that problem altogether.
However, if a dev doesn't think they'll get their $100 back from Steam, I'd be surprised if their game would sell more than a few copies here either. Exceptions might be very niche games with a small but dedicated audience (some visual novels, or asset packs maybe).
I've just realised @hechelion and I have both read your question in an entirely different way, so I apologise if this answer isn't what you wanted!