Des, I've heard that before in respect to Aus delivered cars, though I thought maybe the 4.5's also got the wider ones.
Here in South Africa, all locally assembled 280SE, 350SE, R107 supplied with Bundts got 6.5" items, so they are plentiful here. In fact, the 6" ones are rare, having only been fitted to some W123's it seems. I'm willing to be corrected, but this is my understanding.