It's really becoming the most cost-effective and sensible way to do it, I think. Instead of
re-inventing a complete operating-system to run on your new hardware, you use a good one that already exists. And "open source" enables you to do that (whether the source-code that you use is free, or purchased, or both). I think that we will see more and more momentum building in this direction.
After all, Apple (which is now a household name, at the
front of common retail stores like Target) was able to move their OS/X system quite seamlessly from one hardware platform to another ... and to deliver, not only on their promises, but also on their schedule. Compared to, say, Vista/Longhorn "Windows Not-There"
that's actually saying a lot about the engineering superiority of the approach. Probably makes the investors a whole lot more comfortable, too.