I'm sorry I haven't been around in pinball long enough to become cynical and accept that this is the way things are. I suppose after many years one might become complacent in what they accept. I'm not new to business. You don't need to be Microsoft, or any more than a 1-2 person mom and pop shop to handle this situation however.... And listen, I'm not trying to be a dick here. But if it's considered a "problem" that customers are asking where their product is, than it's a problem with the distributor, not the customer, hands down.
Two low-tech, low-time solutions I have in mind, given that each distributor is selling possibly 10 different machines at any given time....
1) Create a web-page per machine with expected delivery dates and update it daily. Anyone emailing or calling could be directed to check this page whenever they want.
2) Create a distribution group per machine and email with any changes to expecations.
Both of these solutions would (a) drastically reduce the incoming emails, (b) drastically reduce time spend emailing customers the same thing over and over, (c) increase customer satisfaction.
Being new to this whole thing doesn't mean my opinions should be discounted. In fact, as someone who is relatively new to this whole thing, I'm a little disappointed that some of the guys who have been around for a while are so happy with a "buy it or don't" and "it is what it is" mentality. Pinball keeps advancing, why doesn't the market and distribution service as well? It's a shame really.