It's understandable that they chose to do two adventures to start with. Adventures are fairly easy to get going with for a developer, and it will be a way for FFG to get a feel for the system and the world. Also from a commercial viewpoint, they are up against the roll-out of fourth edition D&D during this year. This means that they probably don't want to sink too much money into launching yet another 256 page rulebook to compete for the few gaming dollars going round the block.
The titles, Shadows of Empire and Tomb of Thieves, don't conjure any immediate WFRP images in my head. The first sounds like the Star Wars campaign book I've got in my shelf, and the second sounds like it's a module for Thieves World. I'm sure FFG are aware of this, and will work hard to work the right WFP atmosphere into the books.
What I don't understand is why FFG didn't announce this news at their own website.