I expect what is going on is that the shader has decided to compile the entire expression (identity * world * view * projection), and all of the calculations that go into it, into a single constant matrix.
This is a pretty normal compiler optimisation, since all of your inputs are constant at that point. And then the rest of the shader boils down to a single matrix<->vector multiply, and storing a couple of values.
I wouldn't rely on every shader compiler to get this right, and if you make any of those input non-constant (say, to move the camera around), then you will see a massive performance hit.