Or they simply keep supporting old models with new versions of the OS, even though newer software versions are optimized, and contain new features, enabled by newer hardware improvements.
If you machines have more RAM, you can use a more RAM intensive solution to speed many things up, or deliver a more computationally intensive but higher quality solution, or simply add a new previous challenging feature.
What would be interesting, is how fast to old but high spec'd models slow down. What slow downs are from optimizing for newer architectures, vs. optimizing with expectation of higher resources.