One reason may be because Ubuntu stills expect users to do an OS upgrade - which Dell doesn't have the resources every 6 months - to get newer software. If you want an up to date desktop app, like Firefox, officially - ie, without headache-installs via tarballs or source, you have to upgrade to the next release of Ubuntu. That's a dealbreaker for a lot of support organizations.
That and a Linux terminal is much nicer to work with than Command Prompt.
I would be much happier with MS if they would just release different versions for different needs and let me choose which version of the OS I needed and change it at will. The fact that I can do this with Linux is what made me switch in the first place.
And Ubuntu Netbook Remix blows the doors off of Windows 7 Starter for a netbook OS (I assume that this still applies now that they call it Netbook Edition, also).
The other day I bought an Asus Eee PC 1001P only to find that Ubuntu's netbook edition doesn't work out of the box -- I had to do a bunch of google searches, then compile my own wireless driver to make it work. It sucks that Linux still struggles on the basic stuff like driver support, but excels everywhere else. Ndiswrapper only worked half the time on the eeepc, but I managed to find an alpha version of a native atheros driver that made it work much better.
I wouldn't make sweeping claims about Ubuntu based on a couple of characteristics but since you used the word "accessible" I'll go as far as to say that it certainly applies to Ubuntu apps and updates. The free software is enough to meet the needs of many (it goes way beyond what Windows comes with), and the freedom from the need of AV software help make things faster than Windows.
I love OS X, but also enjoy Ubuntu and have found that installing it has worked well when dealing with Windows friends hit with malware. Some keep Windows around to dual boot into for a few games, but all have been quite happy with all net time and most everything else being in Ubuntu. Unlike OS X, Ubuntu comes with a pretty good assortment of games. That's one of the reasons I often install it even on Macs (in VirtualBox which is a free VM).
There's very little to configure and it certainly has no grief comparable to trying to strip the crapware out of many vendors default Windows installs.
Consumers buying generic PCs certainly should pressure their vendors to offer machines without Windows (and without charging them for it). And if they do want Windows, it shouldn't be loaded with crapware. On many machines that more than doubles the boot time.
There are plenty of fast-enough PCs that end up in recycle bins and at thrift stores because of malware. Instead of a new machine, many could do quite well with one of those running Ubuntu. It's free. Don't be shy, try it.
http://www.appleinsider.com/articles/09/02/09/apples_snow_le...
Ofcourse, those drivers are still curated by Apple. Back in 2004, Apple flirted with the idea of opening up Software Update for third parties, but has since decided against it.
"The computer company fears that third party developers could accidently release buggy or infected software updates, which would ultimately effect the Mac OS X operating system, causing customers to fault Apple."
http://www.appleinsider.com/articles/04/07/13/apple_nixes_th...
Come to think of it, the retail version of Windows has sobered down quite a bit, what with Movie Maker, Windows Mail, Messenger, and Photo Gallery only available for download, instead of being tied into the standard installation.
In the EU, one can even purchase Windows without Media Player and Internet Explorer. I think of the aforementioned programs as crapware, so imo, it's heading into the right direction.
Ofcourse, I'm speaking of the current version, Windows 7, which definitely wasn't designed for underpowered laptops. It's like hacking Mac OS X Snow Leopard to work on a netbook: it might work, but it's not going to be as fast as Android or WebOS on the same machine. On the other hand, Windows XP really shouldn't be shipped with new computers, outdated and unsafe as it is.
Since Microsoft really has no suitable offering of Windows for netbooks, I completely understand why every major computer manufacturer wanted to buy Palm Inc, even besides the patent portfolio.
A properly configured Ubuntu installation absolutely beats the pants off Windows for typical netbook tasks. Fast, stable, no viruses, no freaking installers adding crapware and "toolbars" to your browser. All the software you could ever need on a netbook: Chrome, Rhythmbox, VLC, Skype, Spotify, OpenOffice (if Google Docs doesn't do it for you).
I don't know why they've dropped it, why they never gave it a proper shot. They could have really set themselves apart from the sea of netbook manufacturers. I'm waiting for someone to come along and happily eat their lunch.