that fact that I can now buy a computer that's twice as fast and half as expensive as it was in 2009 tells me everything I need to know about how much Canon has been milking their APS-C chip. sure they've added on-chip autofocus now, but a badly implemented feature does not count as improvement.
I'm really happy to see Canon diving into a whole bunch of new areas with cameras like the EOS M and the SL1, but let's get something straight: the body development team are not (hopefully not) the same guys that are the sensor development team. so there is no justification for the near-zero evolution of Canon's APS-C sensor line.
is there anything inherently wrong with the 18 MP APS-C sensor? no. we were pretty happy when the 7D got released with it, and while it never came close to matching the 5DII's sensor, I don't think anyone really expected it to. the sensor was great then, and is just as good now as it was then. the issue to me isn't really the sensor itself, it's what it signifies from Canon. it's Canon telling us that they don't feel that they need to innovate. it's Canon telling us they think we're dumb enough to think that sticking a t5i sticker on a t4i means it's "new". it's Canon lying to us that we shouldn't judge the chip's autofocus speed on the EOS M because it's pre-production, and it'll get much faster by the time of the actual release.
I don't think the folks at Canon are stupid, but I do feel they take the liberty of thinking that their consumer base is a little dim. the t5i is definitely toeing the line of "let's see how sheep-like our customer base is" and I hope the 70D and 7DII have not been treated the same way.