Yep- it cost $ to pay for the hardware and software to host a site ... supported by corporate sponsors, advertisers, member donations or membership fees. Andy R wants DC to remain free for it's users - so a few ads are how the bills get paid.
However, registered users have the ability to turn off the right column, something else Andy R has provided for us. You might want to read this thread: Turn Off Right Column
to find out how to do it.