I was doing this for a very non-technical user. All I said was that Ubuntu was like Windows but free. Nothing confusing about that (from their reaction).

>there is very little software for it (relative to what is available for Windows)

Yes and no. Games are a big problem. For most tasks that most users perform, there's a web browser, email client and an office suite. Applications moving to the web only helps with this. Bespoke software which manages a warehouse's stock we don't really care about in this context.

>a moving target (both for users and developers - radical changes in UI from one year to the next, libraries that aren't ABI stable for a year let alone 2 decades)

I agree. Distributions should take more care with this or desktop environment developers should call their new DE something completely different and not make the look like a replacement but rather a competitor. Then again, installing an LTS release should keep a person happy for a couple of years. After that, if they're not a power user, there may be little to no benefit in upgrading to the newest release.

>it's too hard (approaching impossible) to make real money from Linux software.

Tell that to: Sun (hah, great example), RedHat, Google, Apple, the countless software agencies developing on an OSS stack, all the businesses in the world running on a network backbone mostly composed of open software and all the research projects using fancy supercomputers running on Linux. Almost everyone uses Linux in one way or another and almost everyone makes money. Redhat is proof that you can directly use Linux to build a billion dollar business. It's a young business model, but it works well.