Oh come on, this is not a justification, it's just complete laziness. Just spend the extra 5 seconds copying the repo URL from GitHub. It's not like you can avoid that the first time around when you don't know the username anyway (or on subsequent times for that matter, unless the username is pretty memorable), and you'll have a robust URL afterwards without security holes. And plus, then people can change their usernames without breaking links. The cost/benefit ratio is extremely low.