How about this? It is quite possible for a 20x camera's magnification to be higher than that of a 40x. That means the 20x can see farther which, in turn, means it can deliver more detail for a distant subject.

The critical point is the effective focal length of the lense when it is fully zoomed out. A higher number means it can see farther. The other number of interest is the focal length when the lense is not zoomed at all. The ratio of these two numbers is what the "20x" means. Many camcorders use rather mediocre lenses that have a very small unzoomed focal length. This yields the high "x" numbers that they advertise.

The hard part is finding the effective focal lengths that a camera has. The manufacturers are frequently a bit reticent when it comes to disclosing those numbers.