I wonder if this has anything to do with reddit implementing their own image hosting service.

That, and they took an investment from Andreessen-Horowitz and their 2 years is up! I don't think they were able to make a go of it and the writing is on the wall.

That came around before August.

But it might take some months before that change to reddit reverberates into imgur visitor metrics and on into advertising revenue.

Ah whoops, I thought something else was being implied.