pg actually explains why he disabled it in FAQ: How do I make a link in a question? You can't. (This is to prevent people from using this method as a way of s

pg actually explains why he disabled it in FAQ: How do I make a link in a question? You can't. (This is to prevent people from using this method as a way of submitting a link, but with their comments in a privileged position at the top of the page. If you want to submit a link with comments, just submit it, then add a regular comment.)