Higher end Mountain Bike Shocks and Forks use Air chambers to regulate the sensitivity and compression settings for your bike. By doing this, manufacturers are able to reduce significant weight, removing a steel coil/spring and replacing it with air, and you as a rider are able to fine tune how your bike feels and rides.
Shock pumps whilst looking similar to mini pumps, are used purely on shocks and forks which require very high pressures. They also feature a different attachment point, to prevent air loss and provide very accurate pressure readings. The Topeak PocketShock DXG set the benchmark for shock pumps and is used by many riders worlwide.