  We argue that the recent thermal model of jet launching by young stellar
objects, when applied to system containing disk-accreting white dwarfs
naturally explain the otherwise astonishing absence of jets in cataclysmic
variable stars. Thermal launching is possible when the accreted material is
strongly shocked due to large gradients of physical quantities in the boundary
layer (or at the inner boundary of a truncated disk) and then cools on a time
scale longer than its ejection time from the disk. In our framework the
magnetic fields are weak, and serve only to recollimate the outflow at large
distances from the source, or to initiate the shock, but not as a jet-driving
agent. Using criteria for shock formation and mass ejection, we find the mass
accretion rate above which jets can be launched from boundary layers around
accreting white dwarfs to be ~10^{-6} Mo/y, which explains the absence of jets
in cataclysmic variable stars and their presence in other white-dwarf accreting
systems such as super-soft X-ray sources, symbiotic stars and classical novae.
