i thought the thing with the walkers was due to parents not watching their children and the babies actually going down steps etc, the newer models are wider at the base as well to stop bubs getting into little spots, i do remember hearing of babies going of the edges of porches and down steps in the walkers and thought this is why they class them as dangerous.
as for cot bumpers i used these when my bubs got much older and were able to lift their heads so if they got up against them they could move away as i think it is a suffocation issue.