Is APS-C narrowing the IQ gap with FF?

[Kayaker72]

Ok, I am still getting my head wrapped around this, but I thought I'd post this and get everyone's thoughts. Over on CR there is a thread going where the OP has asked about the difference in IQ between a 5DIII and T4i. His shooting conditions were good light and low ISO. I took a quick look at Bryan's ISO 12233 charts for the 200 mm f/2 expecting to find a significant difference in IQ such as can be seen between the 5DIII and 7D. But instead, what I found was a much more subtle difference in IQ between the the T4i and 5DIII. Then, comparing the 6D to the 5DIII, honestly, I give the nod to the 6D, abeit, not by much.

But getting back to my question, there seems to be steady improvement in the APS-C sensors under Bryan's test conditions: T2i and 7D are similar, T3i bests the T2i and then the T4i is better than the T3i. At least to my eye.

I am, of course, not missing the other benefits of FF and the higher end cameras (dynamic range, better control of noise/color depth at any give ISO, DOF, etc) (I tried to link to individual graphs at DXO, but that didn't apparently work, here is a link to the comparison page). But, is APS-C closing the IQ gap, specifically sharpness and contrast? How is this happening with the "same" sensor, better AA filter?