The ATSC document is a bit of a wade, the EBU one is a bit easier, but I'll try to summarise.
No, no measurement system for loudness is perfect. However, what we currently have in the broadcast world is a maximum defined level (PPM6 - measured on a 10ms integrating meter) that you are not allowed to go over, and a set of vague guidelines from broadcasters on levels (e.g. the BBC specify that speech should be in the range PPM3-5). This allows for all kinds of creative levels of sound, since there is no defined reference level.
DVDs (and Cinemas) do have this with Dolby Digital - Cinemas have a defined setup, and all films are supposed to be mixed in a room with this setup also. DVDs have the "Dialnorm" parameter, which sets the amount of attenuation applied to the output, so that the speech elements should always be about the same volume (between DVDs). This system has been half implemented by some broadcasters.
The new standards (ATSC & EBU) specify an integrated loudness over the whole broadcast which all programs should conform to, measured on a meter that takes into account our perception of loudness. For shorter programs e.g commercials, there is also a peak loudness maximum that cannot be exceeded. In theory, all programs should have the same overall loudness, and the adverts should be about the same as the program. There is little point in dynamically compressing the audio too much, since the result will still need to be level shifted to provide the same integrated level, so all that compression will achieve is to take away the dynamics of the audio, making it sound flat.
Several broadcasters have already implemented this in the US, the EBU rules come into effect next year, most of us who do broadcast sound are working towards compliance now for programs.