Well, first of all, I agree that it was their prerogative. There's no implication when you buy a gun that parts will be available from the manufacturer indefinitely.
I don't think the car analogy works though. People talk about buying a gun that they expect to last for a lifetime--maybe even hand down to their children. Cars, not so much.
Anyway, all of that isn't really what I was getting at. The point is that there has been a shift in philosophy at Ruger. It used to be that if you bought a Ruger, you had a reasonable expectation that Ruger was going to put forth the effort to support that gun almost indefinitely. Not because they had to, but because that's how Bill Ruger felt it ought to be. Not because they promised to or thought they were constrained to--it was just the company philosophy.
Now, it's not like that. If you own a Ruger that has been discontinued, you need to plan to be on your own. Ruger not only isn't making an active effort to support those guns like it used to, they actually took the next step and got rid of the stock of parts that they did have for those guns.
Yes, it was their right to do so. I'm just pointing out that people who are still thinking about Ruger as if it were run the old way have missed some important changes, some of which aren't especially positive.