If your talking emergency lighting.....
The NEC states ('99 Edition, 700-16)
"Em. Lighting systems shall be designed and installed so that the failure of any individual lighting element.... cannot leave in total darkness any space that requires emergency illumination"
As to the "requirements" for bathrooms....ya have to speak to the Fire Sub-Code Official (or the Architect/Engineer) as the NEC does not specify the "locations" that emergency lighting has to be installed.
The "two bulb" thing only is mandatory on REQUIRED emergency lighting; it cannot be enforced on "voluntary" emergency lighting.
(But that's another debate)