Scooter, you're overgeneralizing and trying WAY to hard to make your over-generalization stick. The fall of Sega was due to their failure to manage the Japanese side of the Dreamcast. The Saturn really didn't so much play into their fall. Why do you think Microsoft is hanging in there without Japan? Why do you think, again, NEC and Hudson were doing fine with the PC Engine? And BTW, the PC-FX is what sunk NEC as a hardware company. The failure of the PCE in the US and EU was really not a part of it.
Ultimately, having a multi-national model can help because you can temporarily lean on one or two markets harder to hold up the company when you're having trouble in one location or another. But failing to take the US and EU is not what doomed the companies you mentioned. Their own failures to sell themselves in their home country, Japan, is what doomed them.
Oh, and as I recall, during the days of the Saturn, SOE and SOA largely did have to exist on their own feet. SOJ was more than willing to yank the rug out from under them when they started doing poorly. Yes, the companies are attached, and profits from SOE and SOA went back to SOJ, but SOJ was always quick to stem the losses.