AN has no distributors. They have dealers but the discount is very small - I am one of the few left in the US.
You're probably right on large orders that it's no more expensive to buy from them, but you're way wrong on small orders when buying from me.
I place large orders which makes the shipping hurt much less, especially on small items, and you pay more than me for the parts themselves. That said, if you go to the big resellers in the US who make a living selling parts, the markup is big - of course it is, they are trying to make a living!
Selling parts for me is not a living, it's a PITA that I do to serve the community and to save on the parts I need for my rebuilds. It's also stupid of me to have $70,000 of parts in stock when I'm sure there will still be at least $60,000 left when I die! No, I don't have everything but I'm sitting here right now putting together my next order to replenish everything I've sold since my last order.
That said, I too am a major fan of Andover Norton and am especially happy that they are carrying more and more Triumph parts since I need them just as much as Norton parts.