All pretensions aside, Da Boyz know what's up. The Eldar blabbering about prophecy, Space Marines about duty and the Emperor - Da Boyz, they know it's all about a good fight and the race for a mystical pointy stick is as good an excuse as any.
A new trailer is up for Warhammer 40.000: Dawn of War III titled Prophecy of War. The video is a rough outline of motivations for all factions included in the game, which seem to be Space Marines, Eldar and Orks at this point. Relic Entertainment has a long lasting tradition of including additional armies in Dawn of War expansion packs, so we are likely to see more diverse troops enter the carnage some time after the vanilla release.
The first Dawn of War was a delightful gore-fest with a more traditional approach to RTS design. The sequel went the route of small-scale tactical combat, which might fit the 40K setting in some ways, but it was a far cry from the massive murder fields possible in the first game. Dawn of War III seems to be heading back to the series roots. Everything on display in today's trailer and other promo material suggests that base building will feature prominently and that times of leading around small tactical squads of units are over.
The Orks embody this philosophy in an outstanding manner. Have as many greenskins rush the enemy as possible. Lots of Boyz - with as many shootas, axes, rokkit launchas, tanks and flamers as they can carry and nothing can go wrong.