The application automatically tweets your blog post to the world, thus giving you more exposure. I don't see why you should put down his work when it actually does what it's supposed to.
I use to have this on my website with facebook instead of asking someone to create an account and link it with facebook.
If facebook bans your website => you can't access your account anymore
If facebook crash => you can't access you account anymore
If your facebook account is compromised => you can't access your account anymore
If facebook is blocked on the intranet => you can't ...
there are tons of reason people don't do zero-signup with twitter or facebook.