It's tough to investigate ads that misbehave.
For many many sites, ad-space is sold through several layers before actual content appears. Idiocy takes a while to track down and larger vendors and networks take to binning whole (sub)networks which is incredibly bad for business. I imagine the more savvy ones might be putting SLAs into their contracts requiring time to investigate before such action is done. Unfortunately, there are always ad-makers who don't care and will continue to release badly behaved code.
Wade.
