Dutch here. These vendors have all run into the same problem; their Dutch distributor is no longer able/willing to sell them laptops without Windows 8 preloaded and they haven't found an alternative distributor.
Previously they could buy branded laptops (HP, Lenovo, and such) without Windows. Consumers can already buy such laptops with Windows, and then install Linux on them. These shops made it possible to buy laptops free of Windows, so without having to pay "Windows-tax".
Hettes.nl have received an outpouring of support and have started a petition with the intent to get this practice of product tying discussable in the Dutch House of Representatives and in a well known Dutch consumers' rights television show, and raise awareness of this to the European Union.
They write (my translation):
"At this moment we are receiving many comments about the stopping of Hettes.nl, also on the Internet we are mentioned multiple times and many visitors of Hettes.nl are disappointed that we are stopping. Because of these comments we want to start a petition to make the Dutch government and the European union see that this product tying should stop and that it should be possible to buy computers (any brand) without Windows. So that we can offer computers without Windows to consumers that prefer other operating systems!"
The petition is the link in the last paragraph on this page: http://www.hettes.nl/hettes-stopt
Edit: added translation of Hettes.nl paragraph about their petition.