Why would a computer use the familiar form? It seems to me that I would uncomfortable if a computer, or worse, a web interface actively maintained by team of strangers, started to address in language that suggested a certain level of intimacy.
It might just be my youngness and general disapproval of the polite form speaking here. I really think English has gone in the right direction by removing their polite form in favour of being polite without senseless grammatical contortions.
It's a minor point but actually English has only the polite form. Stiff upper lip, and all that. "Thou" is the singular, but it isn't used much any more.
