I think you're slightly confused. Tons of US spec Japanese cars and parts are made in Japan. When you hear "JDM" it's reffering to parts that are original equipment by the manufacturer sold only in the Japanese market and not available through dealers in the US market. JDM refers to where it's sold, not where it's made. Many of the Japanese spec OEM parts vary from the US spec OEM counterparts so people get them because they look different or even perform better while retaining OEM quality, fit and finish etc.