PCs simply ARE NOT reliable enough and they become obsolete far too quickly for this type of product IMO.
glad you said IMO - in your opinion.
IMO - I disagree with your statement a lot. One simple reasoning is, it is dedicated to do one task for a dedicated outcome, the pinball game. It will not be designed to do anything other than what it is assigned to do , I think 
. where as a PC is designed to try and keep up with the relevant information and new software of the day for what people ask, which generally is too much for it to do.
Also once all updates have been done and dusted etc. etc. ( final code ) why would you worry if it is outdated? It can only be used for this task and this task alone, also like many hobbyist, like us in pinball 
there will ALWAYS be someone to keep the fire burning for the particular format. Christ! some people are still writing software for the Commodore VIC20! remember that one.
All the stuff we fix like system 1, EM's, etc. etc. and others are ALL outdated. We still pursue and achieve problematic solutions, yourself included.
I say embrace technology and see where it takes us.
Cheers
Good argument.
We have a pc at work that has been running non-stop for the last 15 years and it has NEVER faulted (it's a 486 DX2-66).
Pc's are not all unreliable, they are just built to a tolerance that allows for more failures per 100 units.
That's why industrial controllers are more expensive they have similar components but the manufacturing process maintains a smaller fail rate.
So you can get a bullet proof pc that will last 1000 years, only thing is there is less per 100, 1000 or 10,000 units.
It still doesn't stop an industrial or dedicated controller from being unreliable due to poor design as per SYS1 Gottliebs.
