This is not the case in the UK. The Ubuntu version is £199 and in WinXP version £279. The only difference is the HD. It's only an 8GB SSD in the Ubuntu version, but with the £80 saving you can afford to buy a nice one yourself!
I totally agree with the comments that so many advantages of Linux are just not used. One of the first things I did with my Aspire One was to enable all the amazing 3D effects. They are all installed out of the box and work perfectly on this little machine.
I have amazed so many people with this 3D computing environment, all of whom never new such effects existed. Linux has all the WOW power to really get people excited. I just wish it was marketed and shown to the world outside of enthusiasts.
On the subject of Dell offering the Linux version outside the US: I work for a company who is a dell corporate customer. I inquired with our dell account manager when the Linux version would be available. The reply was that it will be available on Sep 22nd. I shall be ordering mine then.