If the part sells, they'll stock it, i.e. "support it"

Next question. What makes parts sell? Field population.

Buy a brand with lots of population in the field (more importantly your field, your country) and there will be plenty of OEM support and an active aftermarket as well.

Buy a brand that is rarely seen in your neck of the woods...you're asking for trouble down the line.

Need an app for iphone? There's probably one out there. Need an app for Windows CE mobile? Good luck.

In Europe, standard is 10 years, although the "Premium" manufacturers like Linde, Still or Jungheirich proudly claim, that they provide the parts for some models for 20 or more years after the end of production.
The fact is, some of their products from 80's and 90's are realy tough "moth....ers", still alive and kicking. So for the OEM's it's a good marketing issue either.

I believe that 10 years for major OEM's is about right. I know many of the major OEM's have parts for trucks back into the 50's and 60's.

So far, all I'm able to find is one OEM that offers 10 years of parts support once a truck is no longer being produced.

Is that industry standard?