I understand why you would want hardware designed to run Linux but wouldn't you still want to do a fresh install so you are less likely to have to deal with spyware/crapware?
edit: have bought two Zareasons and a Dell with Ubuntu preinstalled. The support with Zareason was great at the time, and I'm willing to support companies that ship Linux because they have support that uses Linux, but I'm not going to be running some retailer's OS unless I'm forced to with locked hardware.
1. To know that every feature of the laptop should work out of the box.
2. Ongoing hardware support.
You don't have to keep the supplied OS if you don't want to but what you want is support.
As long as it comes with Linux pre-installed the manufacturer will put resources into ensuring it works or you could return it. That's not the case if you just buy a Windows laptop and wipe it.
Some of these vendors go the extra mile to load up coreboot or some other libre BIOS. There is also some effort put into finding components with solid Linux support. These may be good motivators to buy a Linux laptop, even if you intend to reimage it off the bat.
But if you could go to your local hypermarket and buy a cheap Linux-laptop, I bet many customers would be happy with the installed OS.
The last, and only, time something like that happened was 15 years ago with the Eee PC. I still have mine somewhere around.
Given you are wiping out the OS, "Linux" and "no preinstalled software" are synonymous, but "Linux" is a better keyword.