I think Goldfarb is onto something with the 24mm being the beginning of truly wide lenses whist 28mm is a really wide 'normal' focal length.
I have a 24mm, 28mm, 35mm and multiple 50mm's and i *rarely* use the 28mm. If i'm going after landscape i'm using my 24mm. If i'm walking/traveling i choose the 35mm or 50mm. The 28mm just sits in 'nowhere land' (i'd sell it, but for the $30-$50 i'd get it's not worth selling). Yes, i 'foot-zoom' and can change whats in the frame by backing up/getting closer, but the 'look' of the 28mm vs the 35mm is just *different* and i prefer the 35mm.
Between the 24mm and the 28mm - there's no comparison. They have a *very* different FOV and all of what that entails in a given frame - it's not as simple as backing up/getting closer.