It would really apply to all fuel injected vehicles with a throttle
and multiple fuel injector setup similar to our Volvos'. On older
engines, the fuel and air were mixed by the carburetor and the fuel
kept the intake clean (it is a solvent) around the throttle plates.
On fuel injected, the air rushes past the throttle plate and dirt
and grime build up (more like a slime coating) since there is no fuel
also passing by to help keep it clean.

I clean my annually by just wiping it out with a clean rag with a bit of
alcholol on it.