With that in mind, I can see support contracts as an operational expenditure.
But if "over half of industrial robot purchases in North America have been made by automakers" then that's a lot of capital expenditure. I never got the feel that the companies which make modern industrial robots primarily rented them out (akin to IBM's renting out of tabulation machines 100 years ago). I really thought they mostly sold the robots.
An assembly line isn't really a "product," per se. It's more of amalgamation of several products and technologies, many legacy, that forms a cohesive but loosely-coupled whole. You may have several vendors' products / systems in a line. So what you end up with are ongoing contracts that provide for installation, programming, troubleshooting, maintenance, etc.
There's actually a whole specialized industry that does nothing but design assembly lines. It's pretty neat.
The parent comment mentions that Delta rents their airplane engines. I imagine that they have the capability to do general maintenance on the engines, but that the engines need to be periodically sent back to the supplier (probably GE or Rolls-Royce) for a teardown, safety inspection, and rebuild. Without regular inspections an engine can't be flown, and is essentially worthless. Not much point in actually owning the engine if you can't use it.