I committed to a site on Area 51 which is now in beta. However, when I attempted to log in to the beta site I realized I did not have an account with Stack Exchange. Why doesn't registering on Area 51 for a proposed site create an account for you for the same site once it has moved into beta? (I understand why sites as different as cooking and programming ought not to be automatically linked.)
They're completely different sites, only (mostly) aware of each other through means of human intervention (AFAIK).
Auto account creation for sites (and the dangers therein) was actually brought up recently, I'll try to find the topic.