You're confusing authentication with identification.
Many (most?) web services and software only require the former, not the later. They don't need to know that you're Joe Bloggs, only that you're the unidentified person that created the account and are the one entitled to use it.
This is a more and more important distinction as privacy issues grow.
I think you're right. This makes it simpler. All that is required is an authentication. Right now this is 'input through keyboard' because a keyboard was the only way to provide input. Thinking about other forms of input would help.
Many (most?) web services and software only require the former, not the later. They don't need to know that you're Joe Bloggs, only that you're the unidentified person that created the account and are the one entitled to use it.
This is a more and more important distinction as privacy issues grow.