It's easier and more secure than using a password. Public key cryptography in general is a much better way to do authentication than usernames/passwords. This is just leveraging the existing public key infrastructure and wallet software suite of the Ethereum space to create a community with hopefully a critical mass of users able to authenticate themselves with public key cryptography.
Perhaps another minor additional benefit of making it Ethereum-based is that the Ethereum Name Service allows easy use and registration of human-friendly names as proxies for the public keys.
That's not the problem for something in the blog/message board/social network space. The problem is the ability to generate huge numbers of fake identities and spam. You can make all the Etherium wallets you want.
That's a separate problem, and largely the same whether the sign up method is email or Ethereum account authentication. Spammers can always secure huge numbers of Facebook-accounts/email-addresses/etc.
What this does is make sign in easier and more secure, and obviate the need to keep track of passwords.
Perhaps another minor additional benefit of making it Ethereum-based is that the Ethereum Name Service allows easy use and registration of human-friendly names as proxies for the public keys.