They started enforcing this pretty strictly in the last few weeks. It's a massive turnoff as a service, but considering they're a "social network" now and not just a reddit-specific image host, it's not a surprise.
Ah, the undending cycle of image hosting services. First they start clean and useful, then they gradually degrade in an increased effort to be profitable, then they get replaced by something new that's clean and useful...
Only for as long as initial investor money lasts I guess. There's just no money to be made in 'free' image hosting without starting to do some nasty tactics, mostly involving direct (hot) linking.