Question: why does it seem that the apertures on proposed replacement lenses are getting smaller?Answer: Cost. Adding IS increases cost and the only way to keep these lenses affordable (they are part of the consumer line, not L line) is to reduce the aperture. Canon has the technology to do about anything, but they have to balance aperture against things like image quality, size, weight, features (IS) and cost.
Canon EF 50 f/1.4 to Canon EF 50 f/1.8 IS &
Canon EF 85 f/1.8 to Canon EF 85 f/2.0 IS
It's as if those larger wide open apertures are undesirable but certainly the advancement in technology should make new lenses capable at those speeds?
What am I missing in this line of logic?
To be fair, though, the two lenses mentioned here are both rumors. The actual lenses and their respective apertures haven't been announced yet.
As for the three non-L IS versions that have been announced, two of them kept the same aperture as their predecessors (24/2.8 and 35/2). Both jumped in filter size (52mm to 58mm and 67mm, respectively), although Canon doesn't seem to be very concerned with filter sizes any more.
Only the 28mm dropped from 1.8 to 2.8, which is a shame because a 1.8 with IS would have been a great "normal" lens on crop and would have made a real distinction between the new 24 and 28. But Canon has kept the original 28/1.8 thus far, so apparently they weren't ready to kill that particular darling just yet, despite the sense it would have made. Now they have two 28s in the lineup, which sell for about the same amount new, with the only spec differences being aperture and IS.
Trying to make sense out of Canon lineup decisions is maddening. For instance, why start putting IS in your wide angles rather than your telephotos???