It's not so much a matter of password exposure for people who share passwords with other sites (that is their own fault), it's having to trust all these sites y

It's not so much a matter of password exposure for people who share passwords with other sites (that is their own fault), it's having to trust all these sites you put your password into to keep it secure (you may claim you're not storing it, but how can I verify that). The risk of your twitter password getting out is impersonation and taking control of your twitter account, with no way to recover it. Remote keys have problems too, but the idea behind remote keys is that you enable third party access to the core functionality but the authentication and control of the account itself is out of reach of the third party.