Is there a technical (or otherwise) reason why there are no Sony 1.4 lenses?

I suspect that there's a technical limit. I would like to see a review showing that if I change a 2.8 aperture lens with a 1.4 aperture, for the same focal, object and illumination, I can get two stops in speed! We know that as bright a lens become the wider is the angle of incoming light over the micro lens, so I suppose that, for the Sony sensor, apertures above 1.8 are fruitless. This must be true for all digital cameras, with small changes for each sensor and each lens design. I hope see a review about this subject!