Yes, it's really necessary, because it's a legal requirement. If other stores don't require this information, they're breaking the law. And billing information can be saved between purchases. You have a tab in your account settings for that.
I see. I don't know how I missed this tab in the account settings, that's really useful! Thank you for that.
Why is this information not required when we're paying for a "pay what you want" game, but IS required if the game has a minimum cost? Is it because it's considered a donation and somehow the laws are different?
The paying experience when paying for "pay what you want" games IS what I would expect from an online store - just card number, expiry date, CVC and name, no addresses and other sensitive info. It's also what other stores like GOG and Steam need, and I don't think they're "breaking the law" by not requiring addresses.
P.S. Maybe adding a checkbox "Save Address for future purchases" that saves the info to the tab in account settings would be really useful.