The magnification rating is with respect to the subject size, but the final perspective is with respect to the sensor size as well.
For exampe, let's say a little earthworm is 10mm long. With a digital PnS with 0.45x, the worm's image would be 4.5mm long, and would cover about half the picture (8.8mm long sensor).
On a 1.6x dSLR (22mm), with 0.45x magnification, the worm would cover about 1/5th of the picture. On a full-frame (36mm), the same worm at 0.45x magnification would cover a measly 1/8th of the picture. To get the same *perspective* (worm covering half the picture) on a fullframe, the equivalent magnification would have to be 1.8x.
Anyway, my point is that comparing the magnification factor itself is not very meaningful across different size formats.