That's not really true. Most satellites will only carry out those maneuvers because anything else is expensive and unnecessary. Plane changes are generally pointless for a civilian satellite because they're launched into the appropriate plane to begin with.
Spy satellites are different because the nature of the mission means you can't really guarantee you'll pick the appropriate plane in advance. If something interesting starts happening somewhere in the world, you may want satellites over it sooner than would occur in their current orbits. Spy satellites can and do maneuver to accomplish this. The amount of maneuvering is pretty limited by basic physics and the size of the satellites, but it is done. Here's a page that discusses one:
http://fas.org/spp/military/program/imint/kh-12.htm
"The primary difference between the 28,000 pound KH-11 and the heavier KH-12 is that the additional amount of maneuvering propellant carried on the IMPROVED CRYSTAL. This additional propellant can be used to prolong the operating life of the IMPROVED CRYSTAL, to maneuver to improve coverage of areas on the Earth of particular interest, and to maneuver to evade Soviet anti-satellite interceptors."
A quick calculation: taking the numbers in the article to mean there's 7 tons of fuel on board and 11 tons of non-fuel stuff, assuming the fuel is hydrazine giving a specific impulse of about 220, that gives the satellite a delta-v of about 1km/s, which is fairly substantial.