The tilt does change things, just as focus distance does (and DXO does account for focus distance). The problem is that once you tilt a lens it is no longer focusing at a fixed distance, rather the distance varies across the frame.
I think there is a very good argument for lens manufacturers incorporating EXIF data about tilt/shift. I couldn't agree more about the value of tilt/shift lenses to the art, but that potential will only be realized if technology is advanced to incorporate such metadata. Really, how hard can it be to add? Given the price of such lenses I can't believe that adding tilt/shift/angle sensors would be such a big deal.
One problem with T/S lenses and digital sensors is that they manifest chromatic aberrations of various types (color shift, lateral CA, etc...) due to digital sensors' more three dimensional characteristics as compared to film. These lenses could really come to light with some electronic correction.