yeah , but why is it like this ?!
As Mondoman said, that's the settings that are in the SPD.
Why do they do this? To ensure that the system will boot at the default memory voltage of 1.8v. If you look a little closer and read Corsair's "fine print" I think you'll find that the 5-5-5-12 timings are only guaranteed to work when the memory voltage is set to 1.9v.
Frankly, I never saw the point of going from the 18 Tras to the 12. I don't know what the performance gain would be, but I'm guessing it's very small. So I just left the memory settings at the default values so I could run the memory at 1.8v. I'd rather run a tad cooler than a small tad faster.