There may be someone out there with a definitave answer to this one, and I can only explain this from the view of the car audio industry and what we have also found ourselves.
There are now so many electrcal items in the car these days generating their own electronic fields, that the AM radio signal is getting harder and harder to receive inside a car to the point that it is now being ignored. The standard fit radios are less sensitive compared to the aftermarket replacements that have such fickle tuners, and AM signal reception is now no longer catered for on many sets at all. With FM and digital radio now the way forward, this is what the In car guys are concentrating on.
I cannot find anyone to give an official answer as to whether AM signals are being phased out or reduced in power, but my suspicion is that they may be, especially as just about every other broadcasted signal is being screwed about with as well.
Bottom line is, that if you want to listen to the cricket in the car, or talk radio, then either park up and turn the engine off, or go digital instead.