The first run is limited though, 18,000 copies worldwide. The second production run won't become available until sometime January. GW is hoping to sell big for the Holidays with this by making it limited now, but abundant later. However, they shouldn't be worried about this not selling, as it's an excellent army starting deal, or a great way to reinforce an existing army.
Even Forge World is in on this notion with a load of bundles geared towards quickly and easily (but not cheaply) get you started with their Horus Heresy game:

Legion's Armoured Might - £450
* Base game
* 3x Deimos pattern Rhino
* Land Raider Proteus
* Glaive super-heavy tank

Legion Devastation Force - £870
* 3x Base game
* Achilles-Alpha pattern Land Raider
* Spartan Assault Tank
* Storm Eagle Gunship
* Sicaran Battle Tank
* Typhon Heavy Siege Tank
* Cerberus Heavy Tank Destroyer
* Techmarine in Mk IV Armour
And a task force for every Legion (except for the Space Wolves and Thousand Sons) out there:

Legion Task Force - £225
* Base game
* 30x Legion specific torso
* 30x Legion specific shoulder pad
* 30x Legion specific head