The information stored is proportional to the surface, not volume.
But also, the holographic principle applies to more than black holes. At any volume, the maximum information you can put there is proportional to r^2. That applies to all the volumes inside the volume you just measured... what means that a volume can not be completely full (a weird case of apparent non-locality).
An hologram is a better analogue to it than information being stored on the surface because, outside of black holes it apparently isn't all on the surface. (I guess for the black hole information loss problem, information being in the surface or in a hologram don't make much difference.)
The information stored is proportional to the surface, not volume.
But also, the holographic principle applies to more than black holes. At any volume, the maximum information you can put there is proportional to r^2. That applies to all the volumes inside the volume you just measured... what means that a volume can not be completely full (a weird case of apparent non-locality).
An hologram is a better analogue to it than information being stored on the surface because, outside of black holes it apparently isn't all on the surface. (I guess for the black hole information loss problem, information being in the surface or in a hologram don't make much difference.)