The designers of the HID class seem to have had lots of uses in mind for HID class in addition to keyboards, mice, and joysticks. You can tell by the way the HID spec was written. 

The writers of the HID class spec included things like this:

• a way to encode the units of each data item:
• linear and angular distances and velocities,
• temperatures,
• voltages and currents, 
• even more complicated units can be declared.
• Also, scale factors can be declared which can be large powers of 10.

Think about that: you wouldn’t need units and big scale factors for a device class that was intended to be limited to keyboards and mice.