  Recently, Park and Gott reported an interesting observation: image separation
of lensed QSOs declines with QSO redshift more precipitously than expected in
any realistic world model, if the lenses are taken to be either singular
isothermal spheres or point masses. In this Letter I propose that the observed
trend arises naturally if the lensing galaxies have logarithmic surface mass
density profiles that gradually change with radius. If the observed lack of
central (odd) images is also taken into account, the data favor a universal
dark matter density profile over an isothermal sphere with a core. Since the
trend of image separation vs. source redshift is mostly a reflection of galaxy
properties, it cannot be straightforwardly used as a test of cosmological
models. Furthermore, the current upper limits on the cosmological constant may
have to be revised.
