Because typically what you do in cases like this is win a case and then use that win against others.
How am I over simplifying it? The judge did NOT compare the tab to the ipad2, but to the community design drawing (which doesn't look like an ipad2 either, it's a lot thicker)
So you're right, Apple's not going after others. But apple has this win in Germany that they CAN use against any others if they want to.
So say next year Asus comes out with a windows8 tablet that docks with their transformer dock and it's a runaway success (tablet/laptop transforming has that chance) Apple can use this lawsuit to strengthen the case against them, and this judge will most likely grant it there as well.
So again, how do you make a tablet in another way and still have it be USEFUL (as in, the additions are done for some other reason than to JUST avoid this design) Sure, Sony did it. But read the reviews. They ALL say that while it's drastically improved in one orientation, the design severely limits other use cases.