imgur grew out of the garden that is reddit; it was suppose to replace all those other crappy hosting services. It's been known for a while that directly navigating to a i.com/direct-link.jpg link costs imgur because they get no ad impressions from those loads.
While I think this is the eventual trend of every imgur page load, they are saving reddit for the last as that is the last community they can afford to piss off.
I feel for them though... it is really hard to stomach how expensive bandwidth and storage can get for a "free" media startup like this -- I am guessing they are slowly shifting scope and "growing" though as they hire more people, like every other startup in history... at some point they grow out of that sweet spot they supported (easy/fast image hosting) and into a realm no one really wanted or needed them (but makes them money).
Oh well. Every time a company does this, it leaves the door open for another company to come up behind them and re-solve that problem in another interesting way. It is the way of growth and change.