[Tagging] Is a sidewalk always adjacent to a traversable road?

[Anthony]

On Sat, Aug 27, 2011 at 5:36 PM, Nathan Edgars II <neroute2 at gmail.com> wrote:
> There are also mowed grassy strips within highway rights-of-way that are
> sidewalks by law (at least where used enough to become a beaten path:
> http://www.dot.state.fl.us/safety/ped_bike/laws/ped_bike_pedLaws.shtm), but
> not for the purpose of the sidewalk tags in OSM.

Why not?