These are valid remarks, but a major factor is the nature of the website. The world cup is hugely popular and will end in a few days. It wouldn't even make sense for most users to sign up for a website that will be used every 4 years. On the other hand, if your site needs users' contribution, and the ability to attribute them to them, registrations are way to go.
You would still be able to attribute a contribution to the visitor of the secret link. What lacks for a longer use is the ability to recover a lost secret url.
We would need to invent a system, that would uniquely identify a user say with a name which we will call "username" and a secret message which we will call "password".
We could call it something like "basic authentication".
