Alright 06... to briefly summize coilovers vs. traditional 'body springs' - your correct!
The difference with coilovers is that the shock tube (or strut), which is used to DAMPEN bumps travels through the center of an adjustable coil spring (sometimes coilover setups use 2 coils stacked on top of one another). By adjustable- I mean the coil spring (which supports the weight of vehicle above the axles) can be compressed to lower or de-compressed to raise. These are *manual* adjustments - as opposed to an airbag kit which is done via compressors, air, and bags. Some of the nicer (more aggressive) coilover set-ups also have adjustable SHOCKS that are used in conjunction with the springs... therefore the configurations are nearly infinite.
As for the GL's, they serve the same purpose (supporting the vehicle) and are OEM-type springs... NOT adjustable. They ARE coiled more tightly (compressed) to lower the stock ride height.
Hope it helps!

 

Adjustable coil overs use a threaded sleeve on the body with a threaded collar for the spring seat to adjust ride height. They do not compress the coil more. The spring rate remains the same.

The K&W kit for the HHR uses a threaded adjustable seat in the stock spring location.