I'm actually with you about them finding more cost effective ways to serve all that content. I wonder if they should think about using peer-to-peer caching using HTML5/webworkers and other distributed caching methods. Given that the community has strong support for reddit (they even give money freely via the donation bar), maybe they would be okay with allowing spare bandwidth to be used to keep the site running.
On the ads side, I think the proprietary system they have is not doing them any favors when it comes to getting a piece of the ad spend pie during RFPs. I don't even know how an advertiser would begin to figure out which subreddits they should target w/o having to sit down and dive into all the stats. The other core issue I think is that reddit specifically touts the fact that you target by subreddit not by demographics/users/behavior, etc. but I think that data is extremely important to most advertisers.