  The results of the recently published spectroscopically complete survey of
dusty star-forming galaxies detected by the South Pole Telescope (SPT) over
2500 deg^2 proved to be challenging for galaxy formation models that generally
underpredict the observed abundance of high-z galaxies. In this paper we
interpret these results in the light of a physically grounded model for the
evolution of spheroidal galaxies. The model accurately reproduces the measured
redshift distribution of galaxies without any adjustment of the parameters. The
data do not support the indications of an excess of z > 4 dusty galaxies
reported by some analyses of Herschel surveys.
