Hi Tom,
I don't really disagree with what you wrote, I think we were just referring to different points in time. Not every statement is true forever in all cases.
That said, Shimano road parts haven't changed much in the past few years, look at Dura Ace which has been the same for about 6 years, with the smallest of tweaks. So it's very important to sell the differences between group X and Y, 'cause there's nothing new here. That makes the grouppo important for marketing.
Strangely, shimano keeps adding "non-grouppo" parts to their line, these cranks, brakes, and hubs have no group designation, just a part number. Why is this? Not for some manufacturing reason, but because it's better marketing to have a low end part that just says shimano, instead of "altus" or "acera" when the rear derailleur on the bike is XT.
grant mclean
toronto, canada