Makes sense to me. Much the same way that you can use wordpress.com’s reader if you’re not hosted there, but those who are hosted on wordpress.com get different exposure from others. You can keep the same experience for users while still supplying an enhanced experience for others. I suspect medium has a super high goodwill factor which makes avid fans grateful to join and give back!

Social Entrepreneur | Host of People Helping People | Social impact Coach | Founder of Wild Tiger Tees