Paul,
You contribute a lot of interesting reading to this forum, too, and I often find myself nodding when I read your posts. I too am am a motorcycle enthusiast, and a Skywave (Burgman) enthusiast, and find it a bit painful if people criticise the machine where I felt that it wasn't warranted, so can probably understand why you reacted as you did initially.
My job demans that I travel quite a lot, and I've spent time on the west coast and agree with your and Ted's accounts of the west and mid-west. I was largely in San Fransisco and Los Angeles when we were going though an expansion period in the late 1990s, and also spent time in New York. As you suggest, Tokyo is a different story to even these congested US cities, but some European cities - especially London - make Tokyo's roads feel like a highway. At least you can filter through the queues in Tokyo - everybody uses the efficient public transport system, so it's only commercial vehicles, taxis and motorcycles on the road on weekdays, anyway. In London unles you are riding an SR125 or smaller, you are going to queue with the cars. There are few gaps to filter through, and frustrated motorists will block your path if they can.
The Suzuki Skywave(Burgman) AN250/400, Honda Forza (Relfex) and Yamaha Majesty series were predominantly designed as single market machines - for the Japan market, and the Japan context city riding, with light touring at the weekend. They don't even advertise them as scooters now - they advertsie them as "open two seaters". Suzuki bored out the AN250 to make the AN400 largely for export but it isnt' a truly separate machine to the 250 - and doesn't need to be as the An250 is such a great base. However, the SW and AN650 were designed from the groud up with that little bit more grunt, stability, and carry space for the more open roads of the Japanese countryside and for the foreign markets with the context you have described.
Here, for many people, the big-scooter replaces the need for a car (due to the cost of parking spaces eg 400USD per month at my apartment) and even in the suburbs where parking spaces are cheap (100USD per month) the annual tax on a car make a big scooter attractive. (That's also why they have tax exempt "microcars" here.) The bigger engines of the 650 and SW allow these machines to be real "do everythings" as they can cruise down the highway at an indicated 180km/h without a wobble, and without the engine being near the redline. This speed is significant here, as this is the speed that all vehicles are limited to in Japan, so it gives the feeling that these GT scooter are not low power machines.
As you say, a totally different context.
My advice to any potential buyer is: buy whichever one tickles your fancy. The competition is so stiff now in Japan, and to a lesser extent Italy, that there are no "bad" bikes in the current line-up. Test ride everything, and get what feels good and matches your needs. No choice made after that process will be a wrong one.