When you pay more you expect the product to be more reliable and better working.
My Iwata HP-C and HP-B are the same brush with the exception of different sized paint cups and different needle/nozzles. I can and have interchanged parts between the two. I see that Iwata still sells the HP-A, B and C even after 20 years so they do not change a good design. My HP-C is still as state of the art as it was a radical 20 years ago. That HP-C is not obsolete yet.
When you buy a Japanese product they consider that you are buying into their family. And that family will support you. But to show your support you must buy their product. That is the Japanese way, at least it used to be. I've never had to contact customer support in the 20 years I've owned my HP-C so I wouldn't know how they treat an Iwata user. But I would think customer service would be in the US (you never know nowadays) so if the CS is rude it might be the US representatives.
I would buy American if America had a comparable product. I haven't been proven that yet. Here is an example. I just bought a new Badger airbrush and it came in the mail today. Why did I buy a Badger? Because I wanted to try a new product, the price was right and I wanted to try a domestic product (is Badger American?). As I was lubricating the needle I instantly noticed how rough the needle felt as I slipped it into the brush handle. It wasn’t rough but it was because the Iwata needles are so much smoother. You might be tempted to say my Iwata needles are broke in but I replaced the HP-A needle last year because a friend of mine bent the tip and the nozzle on it. The new HP-A needle felt just as smooth as the ancient HP-C needle. The Badger needle quality was not as good or Iwata makes a more refined product.