I found this whilst doing some searches for my campaigns blog. When I search google for "warhammer 40k campaigns", GW comes up as a sponsor on the right hand side.
Now, they're pay per click sponsored, and if you don't understand what that means, basically a company tells google how much they are willing to pay per visitor that google sends via the advert for specific keywords.
So, basically GW is paying for people to come visit their site which seems a bit strange as you'd think anyone searching for 40k stuff would already know the GW site. I also noticed that they seem to be paying more than wayland games.
The only thing I can think of is that they're hoping to pick up traffic from those people who are looking to buy 40k stuff as an xmas present and they're not aware of the GW main site and just searching for little johny's xmas wishlist.