Well, they will still have to import all the upstream changes, and make sure that all the parts play well with each other, which, they can still do. Except that

Well, they will still have to import all the upstream changes, and make sure that all the parts play well with each other, which, they can still do. Except that they don't. I think what makes it hard is the dizzying variety of CPUs that makes it all hard to keep up with. I have heard from insiders that as far as manufacturers are concerned, a CPU stays "current" for about 6 months.