Is it not about change and focus?
Within the non-"I like to work on my computers all day to make them do what I want them to do" group (consumers who just want the computer to work and not have to spend more time getting it to do what they want to do than actually doing it), the real problem with all software is change.
Versions and updates change rapidly and sometimes just as you're getting something to work well for you, the rug is pulled out from under you and you have to start looking for something else to do the thing you did so well on the previous platform (usually this is related to hardware change - drivers in particular - but sometimes software as well). If you aren't into the searching and tweaking, that can be a nasty proposition.
Closed systems seem to mitigate the problems of change by managing them for us. AKA MS Windows changes frequently, but the underlying systems are never far from where they were even several versions ago, and for the most part there is a backwards compatibility and a hardware testing process that allows you to continue to use older software or at the very least files, in ways that are still useful.
Yes, all of that is true with "open source" but keep in mind my comments about not wishing to have to continually tweak the software, but just have it work.
Ubuntu has come a long way in trying to mitigate the changes and manage them as a whole (rather than simply as smaller components) in the same manner as MS & Apple have, but without the huge corporate monster eating up people's wallets, but it is still lacking in the focused direction those companies have.
I hear a lot about Apple and MS embracing the Open Source community and learning from their model to improve their products, but I don't think I have ever heard of Open Source learning from the Closed systems to improve on their own model... or is that what Ubuntu was all about?
I hear about the lack of advertising of the *nix OS's a lot - why can't someone - perhaps even for a few $ that could be paid by the hardware vendors - pull together a managed system that is useful to the non-technical, consistently managed with clear direction and a user focus, driven by user focus groups and feedback rather than the technical whims of developers (that should still not be lost)... that is the challenge for Ubuntu I think.
That too (to some extent), appears to be Google's approach, and it seems to be working for them.
Sorry for the disjointed thoughts...
