Truth is, they matched the current output of the generator with the regulator. If your generator produced 30 amps, then you need a 30 amp regulator. Some guys use a Jeep regulator in a jam because it works.
Regulators simply cycle the field power in your gen, which causes the armature to produce more or less current. Regulators have a 'cutout relay' that disconnects from the battery when the key is off, so your battery doesn't drain over night.
Make sure your GEN light bulb works. It 'jump starts' the armature upon starting. - Dave