GW Pulls support from the independent tournament scene.
After October this year, Throne of Skulls will be discontinued and GW will no longer be providing any prize support or other support to independent tournaments and events. (such as Adepticon).
The only possible reason I could see for doing a move like this is that they want to have everything run through their stores and they don't want to be supporting events that possibly have competitors products at the event.
This is a very tenuous reason at best because the independent tournament scene has been doing quite a bit at building communities and providing a lot of business for GW. Who do you think buys the latest codexes and armies, therefore giving the most business?