No, you can worry because you always need some spare parts of you ride a lot (by this I mean all year long and by all weather conditions etc...) but after a few years you can't get spare parts for the top models.
This is the case for example for "old" Dura Ace parts, they are not available to buy anymore, you just get a standard spare part.
And for old Campa parts that's even worse I heard.
Now this is a common situation but the OP is pointing out that this situation may arise sooner than in the past because the industry is changing the standards more often - yes it is marketing. The more often you change the better for the $ industry. That's the game
By the time you won't be able to get spare parts, you likely won't care anymore. Are you still complaining about moving on from friction shifters, 5-speed cassettes, etc? Should bike companies just cease to innovate then? Or is it only innovation when it is something that you (et al) have "deemed" as being worthy?
Unless you are some small niche builder with a waiting list that will keep you going for years, it's innovate or die, that's the way it works for most businesses, whether it bikes, cars, electronics, appliances, etc., it is not some nefarious plan to screw people out of their money.
And having thousands of $$$ tied up in spare wheel sets and other standards is not a problem a lot of people have, silly to think bike/component manufacturers should abandon innovation to appease a minority of people. If there ends up being a demand for rim brake spares, and there likely will, it will be supported.
And up until about 6 years ago I rode the same bike for 16 years and I can still find parts for it. Several bikes later and I now have a disc brake TCR and love it, have not found any of the "issues" people like to go on about to be true and like the commenter above I will not be going back