PPM ain't gonna be perfect, but it's gotta be better than the diary method!!!! I think because it's a whole new way of measurement that it's just going to take a while to learn how to read it all. For instance, you'll just have to take into consideration that a lot of incidental listening is going to be factored in. That's going to make the cume larger and lower the TSL. Doesn't mean that the typical listeners to that station listen a lot less, there's just more sampling involved in the average.
As for malls, things have become way more sophisticated and very few stores still play the radio. It does happen, but not nearly so much as 10 years ago. The big chain stores dictate the type of music that's played because they know what fits their demographics. It's highly researched and they play music that makes people buy! They're not going to let some hourly part-time employee play what THEY want! Doctors offices are the same. If they're small, they might play a radio station, but most clinics have some kind of sophisticated health radio thing going.