User Registration

So I was on News.com, and I was checking out their news alert emails (I won’t bother asking why this isn’t available in RSS), and was presented with this form.

My question is, why doesn’t a log in form like this actually double up as a registration form? Then, if the site really wants more information about me, it can request it (although unless there is some form of incentive, it’s unlikely I’ll respond). It obviously won’t work for every site, where more information might be necessary (shipping info, for example). But in fact, if that’s the case, why bother asking me to register at all? “Here’s my email; send me stuff please.”

And if I need to edit anything, I can click a button and you can just me a one-shot link to my email to verify that it’s me.