  We present an explanation for the puzzling spectral and transport properties
of layered cobaltates close to the band-insulator limit, which relies on the
key effect of charge ordering. Blocking a significant fraction of the lattice
sites deeply modifies the electronic structure in a way that is shown to be
quantitatively consistent with photoemission experiments. It also makes the
system highly sensitive to interactions (especially to intersite ones), hence
accounting for the strong correlations effects observed in this regime, such as
the high effective mass and quasiparticle scattering rate. These conclusions
are supported by a theoretical study of an extended Hubbard model with a
realistic band structure on an effective kagom\`e lattice.
