I think this is they key. GW is releasing a game that can be played on its own, used as an add-on to any existing army, or used as the start of a new army.
Either way I like what I've seen so far.
I like it too. Thats one of the more interesting things about 30k, a lot of the armies can use all the same models, but the color schemes and compositions dictate which legion it is.