Each lens is designed to varies in convergence point onto the sensor and the Canon Top-notch 1D Mark III even has a built-in function to correct and register them! Now, that brings me to question how the Nikon D90 accomodates such discrepancy.
Today, I am told by the Nikon Service center that they do have a sophisticated diagnostic software to verify this and that some sort of corrections will be made if a problem is detected! Interesting indeed...
Let me send my camera in to check this out soon.