I have a feeling the link to the source code was taken down after people started taking the piss out of the quality of it. You can still find it here:
http://www.benheck.com/Downloads/amh/AMH_code.zip

What I would like is companies properly following the GPL/open source licenses. For example, Big Guys Pinball ripping off QEMU, PPS also were playing a bit fast and loose with what they were doing with their remakes.

TBH I have no idea why the link to the source was removed, just a wild ass guess seeing as the rest of it was left up there, just the main game source was removed.

At the end of the day, Ben is a jack of all trades, so it's not a personal dig at him. Hell the first time I wrote pinball code it was downright embarrassing, but it's a learning curve. Just a real shame that Spooky don't go for something like Github for source revision control, rather than lumping it all into a single file. It would mean that the community could work together to make it better.

EDIT: It seems some of the files are on Github, just not the main game code:
https://github.com/LonghornEngineer/Pinheck_Pinball_System

There is a valid business case, MPF and Gerrys offerings both have an open source component to them:
https://github.com/preble/pyprocgame
https://github.com/missionpinball/mpf

As for ROI, it means they have libraries with more features/bugfixes etc, meaning the hardware they sell is more attractive. But this is something that will only ever appeal to boutique makers, not to someone like Stern/JJP.

Like I said, open source *components*, in the example of Lexi Lightspeed, it'll be using some form of pyprocgame, which has contributions from the P-ROC community.

In any case, both Stern/JJP use open source software in the form of Linux. I know it might be hard for you to understand how a business can make a profit from producing open source software, but many do.