Just to address the OEM point, most machinery is OEM built and plenty have simple PLC programs running in them. Some use locked programs some don't. Some are very large and complicated machines and no one tries to fiddle with them while others are simple and obvious how they work.
The ones that have a simple function are the sort that TriPLC is most suited to and are also the ones that are sandwiched in the middle of bigger equipment acting as glue or atleast that's what the management are expecting to happen. Being able to tweak such a device is a desirable abillity.
It's also common for these to be a one-off contract job that is slapped together and the "official support" soon fades away. The software is not stored anywhere nor documented properly, relying on the ladder diagram to be the documentation. Being able to edit the PLC contents directly is a very common situation, often having to later makeup the labelling for the I/O also.
Evan