Well it kind of does.. A password is validated, and if you lose it there is usually some recourse. Reset or whatnot. It may be a hassle but always possible somehow.
If you lose a passphrase, no one can help you even if you hit HN front page and /r/all with a sob story. So backups and availability have a different cruciality.
Also if you store a private key on the same medium as a password store with weak encryption or key that contains the passphrase, they key can't be considered as strong anymore.
There are practical reasons to make a distinction and mistakes can be expensive.