Situation 2011: In USA most microphones are dynamic and use 4-Pin connectors. In Europe President and (some) Midland models use a 6-Pin connector. President is also using electret microphones on all models now.
When using a dynamic microphone on a radio built for using an electret microphone, the modulation level will be lower than with the original mike. BUT if it is a power mike (amplified) there will be no problem.
The cable makes it also a lot easier for shops to test and demonstrate different models of microphones without the need to solder a connector to a microphone just for demonstration purposes.