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???
I think the decision about the 28mm lenses make sense. Canon has two options:
1. Kill both the f/1.8 & f/2.8 versions, and sell a 28mm f/1.8 IS USM. Canon sells only one lens.
2. Upgrade the f/2.8 w/ IS & USM, and keep selling the f/1.8. Canon sells two lenses, one having already covered it's expenses, allowing customers to choose between either a 1+ stop and IS & USM.
More importantly, the 2nd option leaves a wider margin to release an L, e.g. EF 28mm f/1.4 L USM. A lot of people would rather have IS over a fraction of a stop, especially if neither have weather sealing. Make the difference two stops, and things look a lot different.