Since the sensor doesn't actually detect light from a fast cone, it can't contribute to the bokeh
I'm not sure where you read this, but it's demonstrably false. I'm looking at two 7D + Sigma 50mm shots on my screen right now, f/1.4 and f/2, same subject/distance/etc., and the difference in bokeh is quite clear.
Apologies for trimming your post.
First, I'm well aware of the LL open letter and have referred people to it previously - here, on POTN and elsewhere.
I observed four effects -
1. Few people bothered to go to read the reference and digest its content.
2. It refers to a DXO study and there's a rabid hatred of DXO measurements, particularly since they tend to be quite scathing over Canon offerings.
3. Few people who read the letter did any testing but this did not prevent them from commenting that it was a lie - perhaps a result of point 2.
4. There was a lot of nastiness - particularly from owners of 50L and 85L lenses - perhaps because they had a lot of dollars sunk in the lenses.
Because of this, I've changed my approach. I invite people to perform the experiments and simply judge for themselves. It cuts through the internet noise quite effectively.
Ok, so let's assume you've now performed the experiment using a 7D.
If you did it properly, you will have noted that the image is dimmer when the camera could not communicate with the lens. I venture that the same number of photons hit each pixel (within photon noise and your ability to align the tests) so presumably something else gets changed when the camera communicates with the sensor.
There is simply no way that a photon that is not detected can plausibly contribute to the bokeh. (If you doubt this, please suggest a mechanism.) Therefore, if there's a difference between in the image quality between (say f/1.4 and f/2), it can't be light that's doing it.I strongly suspect that there is some image processing going on inside the camera to deliberately soften the image from lenses that have large apertures.
It may be possible to demonstrate this idea by installing an aperture mask on a wide open lens and seeing whether the image quality changes (say between f/1.4 and f/1.8.)
Finally - another reference that may be of interest http://goo.gl/5We9r
. Note how the 7D loses 0.65 EV when the sensor is illuminated by a f/1.4 lens. This strongly suggests that the pixels do not respond to light that's coming from a cone which is faster than f/2. Similarly, a 5D2 and 1D4 will lose 0.44 EV at f/1.4.