Well not really the architecture drop happens at the same time for all platforms afaik (certainly did in the past).Please refrain from posting "Sky is falling" stuff when it can be avoided with ease. There's a large difference from "dropping Catalyst support" to "dropping FGLRX support in Linux".
That said, there are still the legacy drivers, and with windows it's not _that_ much of a problem. It means on linux some new xorg or kernel version will likely break compatibility but you can keep running it on your existing windows version.