One day a blockchain might be gone, or so many forks might happen that you don't know who to trust anymore. It's all about who & what to trust. There're shops that do not care at all about that paper for the warranty (emag for example), as they have it all in their database...
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Emag is an online shop (like Amazon) so it comes naturally to them. I'm talking here about brick and mortar shops which do not naturally ask your name and address when you buy something.
Because it's not "in the mores", a brick and mortar shop needs a reason to ask you what's your name, birth date and perhaps ask for ID. Establishing a warranty is a good reason. But there intervenes a chicken and egg problem because if they invest in a customer database and do not manage to recoup the cost by selling enough extended warranties then their viability is even more in danger. Steem might offer an economic alternative to developing a full custom system by bundling together more functionalities at a much lower cost than a custom built warranty-management system.
But the points you raise are valid