A lot of those multiple run machines were produced in smaller subsequent runs after the primary production run based on specific requests from 80 pound gorilla distributors. There is often a perception that there are so many of them out there (POTC is another one). That webbed siderail version SM you have PBP was done at the specific request of Betson Amusements. Smaller distros like KJWHF in Perth and AMD then piggybacked off that order to boost the numbers.
Stern supposedly only needs an order of ~100 units to justify putting a title back onto the production line as a one off run if the customer has some clout.
My prediction is that ACDC was and will remain the high water mark due to as Strangeways said the price point. Entry level machines (Pro) need to be priced at $5kAU ($3kUS) to get sales figures that will ever cover come close to matching that. Anything priced at $7k or above and people will simply turn to alternatives at the same price point (i.e. A list Bally/Williams titles) - particularly considering how much Pro models drop in value over the subsequent 12-18 months after unboxing.
