The empirical evidence denies your position. Ubuntu is an improvement measured in light years when compared against, say, Slack 3... or Slack PERIOD... And I love Slack. If an Ubuntu Live CD runs your box well, it is very unlikely that you will have any significant problem with it thereafter. I should know, as I have Ubuntu on quite a few 'user' level clients' machines. I have experienced virtually *no* problem scenarios, and I have been doing this (setting up Linux user level desktops) for years now. Most of the trouble is getting them out of their pre-existing microsoft mentality. A LOT of hand holding till they get it, but really no troubles. And to date, I have only had ONE person ask to go back to Winders.
Modern Linux is nearly up to par with the commercial OS's wrt 'user friendly', though I admit it still needs some work in that area... mainly in the area of gui interfaces for things that most geeks find too easy to change in a config file - but then, while I recognize that fault, I also see the same thing in Windows - There are many tweaks to windows that users find daunting - but that geeks find simple. To the average user, if you ask them to open RegEdit they will go all verklept and flop about on the floor, spewing vomit till they wind up under the desk sucking their thumb... So it isn't that one is better at it than the other, but more a matter of perspective. Personally, I find the registry in windows to be a useless method and thoroughly wish that they would go back to inifile based settings - like back in the Win3x days... something very much like what linux does under the hood.
And that is precisely why Linux will never be more than a niche product on the desktop/laptop market. Linux makes an excellent server for some applications, but the desktop is an entirely different matter. When something goes wrong, where is Grandma going to get help?
Outside of web servers, Linux is having quite a bit of success on mobile devises in its Android incarnation. That's because Google make it extremely easy to use. As for the Linux incarnation of Chrome OS, it's still too early to tell if Google will be successful. But I think Google has a better chance than the typical Linux distribution.