To me, eliminating the outside distribution model creates the same problem for pinball manufacturers as it would for most other industries...getting your product in front of people. This isn't the pillow guy on TV hawking directly to customers for $30 pillows. And they're not Apple with a fanatical following of customers that generates enough revenue to open your own "distributors" (what is an Apple store if not still a distributor that is wholly owned by the company) in every town.
In my opinion, the market for these products can be broken down into 2 very broad segments...Type A and Type B buyers. Type A home buyers have the resources and mind set to buy every new title, sight unseen, that sounds interesting to them...putting deposits on an LE the day it's announced. Ops surely buy new machines sight unseen as they have to keep current to keep drawing the customers. But do all ops buy every new machine? I doubt it. Distributors are just an additional cost to these buyers, and I'm sure they would gladly do without them.
However, Type B buyers have limited space and resources (either literally limited or rationally limited) and are unwilling to shell out thousands of dollars without knowing specifically what they're getting. I believe these buyers make up a significant portion of the pinball market. They want to see and play and interact with the machine before purchase, as well as have direct contact with someone who will be there down the road if they need them. That's the driving force behind distributorships in most industries. No one wants to pay the "middleman", but most people aren't able or willing to buy directly from the manufacturer without laying hands on a product close to home.
I'm a flooring retailer, and the same applies. Distributors (or wholesalers and retailers) serve a purpose that average manufacturers can't replace or don't want to deal with.