Yes, it is easier to say that "such and such" built more! 
The 18,000 B-24s alone is probably more industrial effort than all that list combined.
I am by no means saying that other nations didn't produce very significant aircraft totals, just that the oft used "There were more of x American aircraft than y Japanese aircraft, so obviously the American one should be added first!" argument is correct in regards to production totals, but it ignores the bigger picture in order to use simple production numbers as a justification to have the planeset extremely lopsided in favor of American units.
I remember a guy posting, probably back around the time this thread was posted, that the rule should be that no aircraft with less than 3,000 built should be added. I tore into him based on his arguing for something that would produce extremely biased results. I think he did it in innocence, not realizing that such a rule would only allow two or three Japanese aircraft (A6M5, Ki-43-II, Ki-84-Ia) in the game at all. People put too much stock in production totals. Yes, it is relevant at a point, but by the time you're looking at a couple hundred airframes you have an aircraft that very well could have played a significant role in WWII. The H8K in this thread had less than 200 built of all types, but it served constantly through the whole war as compared to the P-63 which was built in the thousands and
might have fought in limited numbers for a few weeks. Which is more significant? For those who simply judge based on production numbers, the P-63 would be seen as vastly more significant, but from any historical perspective the H8K was the much more significant aircraft.
Basically, production totals are just one factor that needs to be considered. Significance during WWII and difficulty in adding it due to graphics work (B-29 and H8K both get hit hard by this one) or difficulty in getting performance data (Japanese and Russian units have a problem with this one) all play a role as well.
