it's the size...
the bigger your baby is, the higher the class..
BUT 1 impt thing, FZ20 has got hotshoe, makes it DSLR like. but all prosumer cam ba.. coz got aperture control, shutter control, manual control..
compare to a $700 ixus where u can only PnS, go to night mode, and the flash works for about 1 m etc... you have a clear distinction between prosumer and compact.