Choosing an Embedded OS for Sustainability?

vivekb asks: "I work for a small start-up that's building its first commercial product. Because cost is less of an issue than development time, we've decided to make the brains out of an ETX computer with some sort of (non-realtime) operating system. Based on initial costs of tools and estimated license fees, the cheapest OS's I've found are Windows CE and several offerings of Linux. The big question that I can't answer is, 'How much will these platforms cost in sustaining activities?' In three years, when we're fixing bugs or applying patches, how much will we be paying vendors and how much will we be spending on internal developers? When the Linux kernel is at version 3.0 and our device is still running 2.6 -- or when CE reaches .INFO and we're still at .NET -- will support even be available? If anyone has past experience picking an embedded OS for a screen-and-button based electronic device, what did you learn to stick with or avoid?"