He said user content so that might be users uploading images, audio, or video with the associated storage and bandwidth costs not to mention workers for generating thumbnails.
If my costs were anywhere close to that I think I'd have no choice but to suck it up and place some ads as well. As it is, community donations cover our costs just fine, but pretty much 100% of that revenue - which is all of our revenue - goes to infrastructure cost. We don't make any profit, but that was never the intention when creating the sites.