This is a question that I'm curious about. I know it was common practice/policy of Nintendo to only let american games use a certain and limited use of mappers and sometimes this would result in a loss of quality. Take for example Rygar and Argos no Senshi as apparently the sound is much better than its american counterpart. Now there's one NES game that the jap version uses mapper 80 and the american version uses mapper 4. Would there be any significant difference between the two? I skimmed over the mapper doc, but I was unable to find what I was looking for.

It was probably due to the lockout chip being employed as an antipiracy measure in the NES, which wasn't present in the Famicom.  So other companies could make whatever cartridges they wanted for the Famicom as long as it fit in the slot and had the right pinouts --whereas on the NES you needed a special chip on the cartidge to act as a key for the game to work.

Some companies (Tengen and Camerica come to mind) made their own little ways to defeat the lockout, but it seems nearly everybody else just got their boards from Nintendo.


In any event, 080 and 004 tradeoffs:

- 004 has a scanline counter for IRQs, 080 does not
- 080 might not allow SRAM/WRAM (though I doubt emulators will care)
- 080 has three 8k PRG slots swappable, 004 only has two 8k slots

And of course... 004 will be supported everywhere and is easier to find real hardware for, whereas 080 is more obscure.