I’m about to purchase a license, but wonder why on earth you need all that information from the buyer? Isn’t email adress sufficient when paying through Paypal?
I would surmise it is to access the backstage, along with keeping piracy to a minimum. As soon as a registered version is released into the wild the account can be disabled very quickly. Pretty smart really.
Yeah, but adress and personal details? Not that it’s really a problem for me personally, but as this is a downloadable product I really don’t see the need for giving away street adress and other personal info. A lot of people don’t really like giving such info away everywhere, so I can see some potential customer loss. But I guess the advantages outweigh the minuses?
… so they can send the black helicopters 
No, for reasons like: if you loose your backstage password we have some information we can check against the requester before we pass out a new password to log into the backstage.
It is just a security measure to prevent someone else guessing a correct email address and simply requesting a new password to get on the backstage server.
I liked the explanatiion with black helicopters better. 
You will swallow that phrase the day you forget your backstage password 
Is this the first time you ever purchased software online? Because this is standard for every type of online purchase, not just Renoise.
Simple answers:
SWREG, the payment gateway that handles all the money (not Renoise) asks for this info. It’s not like Renoise is a bank. This is the kind of stuff SWREG requires, not necessarily Renoise.
“Hi, my name is Kyle and my email address changed. I don’t have access to my old one anymore. Can you change it to this one so I can download Renoise? Thanks.” At least 2 of these types of emails a week, guaranteed. We need some sort of proof.
Good times.