We present experimental and theoretical results on magnetoresistivity oscillations of high-mobility two-dimensional electron systems in a weak superlattice potential. Experimentally, the band conductivity of a sample with a holographically produced grid potential is shown to be considerably smaller than that of the same sample with a similar linear grating potential of the same lattice constant. This is explained by a magnetotransport theory with due consideration of collision broadening effects and the peculiar subband splitting of Landau levels resulting in a Hofstadter- type energy spectrum.