Once again, you are not the casual user/computer buyer.
WTF is ubuntu? I know its a Linux(like?) thing but if I don't know, then I really don't expect the know-nothing computer buyer to have a clue.
A Chrome PC could be a moderately priced and spec'd PC or Laptop at budget prices for those people that don't want the cost of Windows factored into their price or that don't want to pay the Apple tax for machine that can access the internet.
The reason most people still use IE is because they don't know any better (since it comes with the system) or they have to(everything supports it). It's what automatically pops up when you try to access the internet, and therefore to most, it's good enough. Most people I have introduced to Firefox and even installed a few customizations for them hardly ever look back, but they would never take the initiative to learn about and use something they've never heard of and therefore don't know about.
Take me for example. Why would I choose Linux over whatever is already installed on my machine? I know that Linux exist, but why would I use it? how would Linux make my life easier? the truth is, I don't know so why would I bother looking into it? I know that OSX is a technically better OS, but I've been using windows ever since I graduated from DOS, so it's what I'm used to, it's what I know and that is why it's my OS of choice(it does what I need and that is good enough for now).