The only thing I had ever heard/seen when the term (or acronym) JDM is used is when someone with a Japanese vehicle here in the states that has gawdy body kits, big oversized ridiculous wing, and huge ugly "bling bling" wheels with tires that have a profile of about 5 mm gets called a ricer or his car gets called rice and he argues that "No way, it's not rice, it's JDM!" So, sorry if I called it rice or made a rice comment.
So, now that we have USDM and EDM on top of JDM, then it all comes down to complying with that area's laws? JDM would be illegal here then as JDM would mean meant for Japan's market, thus for the laws in Japan and not here in the US. USDM would be vehicles and parts manufactured for the US complying with the laws in the US. We have never had the same vehicles available that is available elsewhere in the world. Just look back in the mid 80's when the UK was in love with the Ford Escort. In the mid 80's, the Ford Escort was an underpowered economy POS in the US. We did not have the Escort, was it Cosworth or something, available. So many VW vehicles and Subaru's that we could not have that was available anywhere else outside the US. So, in that respect, then yes, EDM or JDM would be much much better than USDM, but we are not capable of having that due to the law.
Now 4 door pickup trucks are all the rage here in the US. It's no longer the SUV that is the selling leader. These came about just in the last few years, yet in Australia (and elsewhere?) Toyota has had the Hilux pickup truck (4 door truck) since the late 70's when the Toy pickup has been around. (just an example of something else that was always available outside the US).
So, sorry when someone mentions JDM to someone in the US, because anything that actually is for performance that would be deemed JDM would be illegal, thus they go for the JDM body kits, wings, wheels, etc to attempt to get away from the "ricer" stereotype, thus saying JDM would just be rice.