In foreign languages with a polite form of "You" (such as French or German), there is an additional question: should a website use the polite of familiar form. And it's widely accepted that a website should use the polite form.
Why would a computer/website be polite to me? They have no concept of these things. Just using polite forms doesn't mean you're being polite, you have to mean it. A computer is as of yet incapable of having intentions.