I used to run a fairly large 40K website (Tau Online, now defunct).
I'd regularly receive letters and e-mails from the Games Workshop legal team.
I remember one time, someone had made a simple post on our forums saying they were thinking of selling a short story they'd written based around the 40K World. He hadn't named the story. It wasn't for sale. He was just thinking out loud.
Anywhoo, the GW lawyers contacted me: they asked me to delete the whole thread, ban the user and provide them with the poster's IP address, name and contact information. Which, y'know, is a bit overkill. (And possibly not legal? We didn't have their name nor contact information, but I would have assumed I couldn't just hand this information out to any random lawyer).
As in this case, the Games Workshop legal team regularly throw around threats - often with no legal basis.
I hope the blog poster is able to garner enough support to move forward with this. Unfortunately I fear that GW's baseless threats will beat back hobbyists, yet again..