Thanks a lot for the detailed answer. Those numbers are very helpful. I read a bit more about it in itch's FAQ and it definitely gets complicated quickly with VAT, US withholding taxes, individual tax treaties and such. Transaction fees are only a small part of the puzzle.
Viewing post in v0.3.0 - Santorini [Major Content Update] comments
Just FYI - I just did my first transfer of funds from Itch to Paypal (they hold the funds for a minimum of 7 days, then you can transfer it to Paypal if you have at least $5 waiting). It turns out that when you do this, they actually give you way more information... and that information doesn't line up with the limited information they give you until that point.
Before I did the transfer, it said I was getting ~60% of what had been paid. On the transfer details screen, that went up to ~80%. I have no idea why these two values are so different, or if/how you can see the accurate value before doing a transfer. But it gets there in the end...