I agree up to a point, but on the other hand we've seen a situation where the latest OS release for a particular range of phones does not run well on the oldest

I agree up to a point, but on the other hand we've seen a situation where the latest OS release for a particular range of phones does not run well on the oldest model of that phone. Someone made a humorous video recently illustrating the problem. Some support cutoff point for old models makes sense.