I don't buy it. I'm in manufacturing/sales and it has a lot to do with what you can get, supply and demand and the wow factor. Why do Cadillac parts cost more than a Chevy? Its because Cadillac owners will pay more.
John, You sell microfiber towels, drying clothes, and polishing pads...that is a huge market in comparison to Ducati parts or even Porsche market ( I owned a wheel/tire and accessory warehouse for import cars in the 80's before it got popular-- so I have a little experience with this).
Make a set of wheels for a 2001 900SS. Do the development work, make a huge run to make the set-up and R&D worthwhile. See how many you sell in a year. Check to see how many are still on the shelf to see if you have broken even yet. Do the same thing with a GSXR1000. Now do the same thing for a Porsche and then a Chevy. You will find that production run sizes and demand makes a difference in inventory turns and production runs.
Granted some of the stuff that you get through Ducati must go through several levels of distribution before it gets to the consumer. Most of the products are imported using a very weak dollar. I know what this stuff costs and how small the actual margins are. I don't see many people getting rich in the motorcycle business. I see a lot of Ducati dealers closing down because they can't do the volume to support the small margins. Most are just getting by.
My friend asked me how big the Ducati market was while we were at a basketball game. I looked around at the huge crowd and said: "how many people here do you think rides sport bikes here? How many do you think rides a Ducati?" I think less than half of the people in that crowd know what a Ducati is...let alone own one. Now how many people in that crowd do you think I can sell a set of Ducati 900SS wheels too? GSXR1000 wheels? How about Chevy wheels? How about about microfiber towels?
Ducati is a niche market within a Niche. Parts are more rare for these bikes than you think. No one with any business sense is going to make a bunch of parts to put on a shelf with such a small market. If you are looking for aftermarket parts, there are less than a handful of people in this country that even know anything about those parts and only a small fraction of those people that actually stock it.