Actually it does come back to the differences in the Warsaw convention and domestic US rules. As you may note, the last Warsaw convention which most international airlines follow did come up with these limitations, you may also note that the last one was in 1955!! Jets were just starting at that time to exist, let alone be used by commercial carriers. In Europe, the masses did not start flying until relatively recently (en masse) while in the US for quite a long time flying has been much more of a "mass transit" solution. This of course was based on lots of factors (government owners, lot of little states, strict regulation, strong unions, restricted slots, etc).

As things were tightly regulated and bureaucratic, the airlines figured they'd stick with the 1955 convention as with little competition, it was not in their interest to change it.

Therefore, if you want to fly into N. America, you have to follow the rules there (as again the North American air market has traditionally been much bigger than the rest of the world's put together - much the same way that many countries follow FAA regulations even when not flying too/from the US).

As far as RTW goes, sorry is this your first big trip abroad? As far as I can remember, the greater limit (2 pieces) takes priority on any multisegment flight, even RTW.

Now for one of my pet peeves (and I'll give an extreme example here)....... Let's say I fly BA in Biz every week RT for a year between LHR and IST. Let's say that I never check in luggage and only do carry on. That means that I've spent appx $50k on the airline in a year on that particular route and have never checked in one piece of luggage (although I could have carried 3060 kg legally in that time and in reality up to 5000 kg's as they always let you do extra in J on these flights).

When I take a trip with my wife and child for holiday, and am 20 kilos over COMBINED between the three of us, I really really do not need to have some snotty nosed little TRAINEE, berate me that I am overweight and DEMAND that I pay several hundred pounds (of which he does get a bonus - many airlines incentivise their agents this way). I should say that I have never had to actually pay in such a situation, but the pain of the argument is something that I should not have to hear (although this problem is better worse with certain airlines alliances, who "reward" their FF's with extra allowance).