Halo Wars may contain 100% less Master Chief than the rest of the series, but hey, look on the bright side. By hiding both skulls and a new type of treasure – black boxes – the developers have generously gifted you with 100% more collectible items. Feel pretty ungrateful now, don't you?
These items are ones you'll definitely want to collect, too. Just as in the shooters, Halo Wars' skulls unlock powerful cheats that can make the RTS much easier, much harder or much, much sillier. The black boxes, meanwhile, complete the game's timeline and are necessary if you want to understand the Halo franchise's entire history.