You're not wrong, and it's easy to prove. Just go to the page where you create a new Google account, and select "Use my current email address instead". Then go

You're not wrong, and it's easy to prove. Just go to the page where you create a new Google account, and select "Use my current email address instead". Then go to the page where you register to be a Chrome web store developer. You won't see any option forcing you to create a @gmail.com address.