They're using large buttons in the post contents above their Twitter/email blurb (and do so in previous posts), so yet another large button saying "Follow us on

They're using large buttons in the post contents above their Twitter/email blurb (and do so in previous posts), so yet another large button saying "Follow us on Twitter" would just get lost in the mix. So, in this case, a smaller link with a nice yellow box around it is likely a better call to action as it's different from the rest of the content.