Well, if you want to sell me something for upwards of six figures, you'd better be prepared to sign a contract for support that includes drivers for updated interfaces (USB vs. Serial) and updated operating systems (Windows 7 vs. XP or even 98). I wouldn't expect an open-ended arrangement, just enough to cover the lifespan of the machine (the robot, not the PC controlling it).
Suppliers going out of business is a common threat but it hasn't got anything to do with being prepared to guarantee support for your product. If the supplier of my industrial robot goes out of business and no-one else is willing to take up the support, then I'll be replacing my robot as soon as I can afford it. I won't risk running them for as long as possible knowing that the beige box in the corner might give up the ghost any day now and I can't buy a mainboard with EISA slots anymore.
As for discontinuing product lines, IBM continues to support (albeit for a lot of $$$) many of its discontinued lines and many people are prepared to pay for that. In my experience with AS400s, it would have been cheaper to upgrade than to continue maintenance on our ten-year-old E35, but management decided to switch to Windows servers instead (I left not long afterwards).