I think they put as much thought into designing heat control into the enclosures as they did to what color they'd make the thing.
Actually, this is my point. The monitors were coming off of lines for things other than arcade games back in the day. The monitor designers were not even sure of what application their units would be put into. With this in mind, the designers are forced to design for worst case scenario, or to standards handed down to them, which are usually quite strict. They were then put into a cabinet that was designed for security, as you stated, and cooling was an afterthought at best.
Bones cabinet has considerably more passive cooling allowance, than even the best of the industry cabinets. His monitor is brand new. It is also a product of 20 plus years of design for the industry, with many previous mistakes to help refine the design needs. This does not take into account the improved manufacturing processes for components and PCBs that have occurred in the last 20.
With all this in mind, mnay of the original monitors have lasted untouched, for over 20 years, without any particular care given to their needs. I would expect a modern home use monitor to last for many years based on the conditions the old industry monitors have withstood.
Of course, it wasn't my hard earned cash that bought it, so I
still believe testing is in order.