Couldn't agree more (as a Fedora user myself! - Ubuntu is typically the "blessed" distro on these systems for various reasons).
However, "linux support" is more than a chosen distro - it's the supporting code necessary to make linux a first-class citizen on the given hardware (driver support, setup scripts, porting popular software, etc...), as well as support knowledge and training at the OEM (bash is bash, and Firefox is Firefox on Ubuntu, Fedora, Arch or whatever).
As for technical support and training, I can see that being useful in an enterprise context, but again, I honestly can't see the type of people who want to single-boot Linux on their laptop being interested in support and training from Dell, HP, etc. It's been my experience that by the time someone is comfortable enough to use Linux as their sole OS (which many people don't want to do despite being comfortable enough due to needing Windows for other reasons, like gaming), they aren't really going to need or want any tech support from an OEM.
On the other hand, I've yet to find a distro that pre-installs a GUI with configuration and packages anywhere close to what I want in a setup. I go out of my way to use distros with an option to install without a desktop environment even if it has an option to install the one I want, since it usually comes with a lot of extra crap I don't want. Obviously I'm probably a little more extreme here than even most Linux users, but at least among Linux power users (i.e. the people I'd expect to be interested in buying a laptop to single-boot Linux) that I know, Unity is considered to be kind of terrible.
Am I wrong in assuming that these types of "developer edition" laptops will generally come with a vanilla Ubuntu install? I admit that I've never really looked into getting one, so it's quite possible I'm mistaken in understanding the kind of setup they provide
> The Dell XPS 13, for example, is a great looking machine - but too many folks were busy buying macbooks to help Dell learn this market segment does indeed want more products like this
Not sure about the why other (potential) Linux users might not buy notebooks such as this, but despite single-booting Linux for the past several years, I wouldn't be any more likely to buy a computer with Linux pre-installed on it because the chances that the computer has a distro/configuration I would want to use is basically zero; if I'm going to have to reinstall Linux and/or configure it from scratch, then the fact that it's specifically marketed as a Linux laptop doesn't really give me anything. I suspect that this might be at least partially responsible for "developer edition" laptops failing, as at least in my anecdotal experience, many people who are looking for an out-of-the-box experience aren't generally inclined to use Linux as their main OS in the first place.