Bodywork costs a sh*t ton of money to develop, manufacture, and maintain spares for. Any vehicle sold in the US is required to be supported for 7 years from the date of introduction...... spares, for those vehicles have to be provided.
Every place a manufacturer can reduce cost, improves the bottom line. Thinner tires, parts that never break (less stocking involved), universal applications for complex parts --- how many places does a mfg use the same ECU, POSSIBLY with different programming?
It's 10 years for Australia with regards to car parts. Not sure about motorcycles. Either way, it's an expensive game!
ECUs definitely have different levels of software.
For the '03 - '04 I've counted maybe 10 or so including the RR variants.
The USA would have at least 2 these days I imagine, one for California vs. other states, if not more if there are other state specific requirements.
Which again is different to the Euro/Australia variants; at least with the Hondas, you guys had your ECMs heavily detuned due to your emissions requirements. I cringe when I see the stock 09+ CBR600RR dyno graphs coming from the USA.
France used to have a 100bhp limit, so that would have been different to the rest of Europe, no longer though.
If the Cluster has any regional variations, that would also be a different part number because that's a separate ECU. I do know for my old CBR600RR, the Australian model did not permit a change to mph reading, because we have no use for it here. However, the USA model did permit changes between km/h and mph, I assume due to cross-border travel between Canada/Mexico.
I didn't look at the part numbers but I imagine it would be different.