What is the typical product life cycle of a new bicycle/groupset? I've heard that some cyclists sell their recent bike when a new groupset becomes available and get a new bike every so many years. I suppose that's one way to avoid terminal parts availability and minimize the cost hit of a new bike, but I don't know if that's a more expensive route than being forced to buy a new bike every 6 to 8 years or what.

If parts availability was not an issue, I could see bikes being well used for many years. But even if you could find new chainrings, you may not be able to find new brifters that work with the groupset should you need to replace one or both... so still an impasse.