Yeah, but to get that 5% you need to use real shitty (read: low compression) codecs. That means a 190MB RAR file for a 200MB video that lasts two minutes at best.
RAR-ing MPEG-derived format files ususally removes a few kilobytes, and I've seen cases where the compressed file was acutally a few bytes bigger than the video file inside it. That's because those formats leave nearly nothing an external lossless compressor can work with.
Of course, if you RAR RAW video that contains little to no movement (like a slide show, or a screen captured tutorial of someone using MS Excel), the compression will skyrocket to over 90%. But that's hardly the case with TV ads.