Create Mashable Follow-like Facebook, Twitter login/connect?

Question

Hi want to ask if anyone can share an idea on how Mashable registration works? Basically the only option you have to register to their site is by Facebook or Twitter, after you login to one of them it automatically create a wp_user. No more Wordpress login/Regs needed.

I know many plugins like Simple Facebook/Twitter/Google connect ^* are available, but i haven't found any plugin related to this one like Mashable have. If anyone can help me on this that will be great.

_{[*] : Simple Facebook Connect, Simple Twitter Connect, Simple Google Connect — by Otto}