Accoustic absorbant material / dampening does help to reduce PC noise. BTW: I'm not particularily aware of the differences between the two terms and use them interchangably. And all my dampening material is expected to be reasonably accoustic absorbant material anyway; it's not like I'm going to use aluminum or tin to dampen my case.
IMO there is a bit of a difference if by damping you are referring to mass damping:
- Mass damping is adding weight to something to stop it vibrating so easily.
- Acoustic foam (i.e. acoustic damping) is designed to reduce the perception of sound by absorbing certain frequencies.
Acoustic foam is often quite heavy, so it serves as a bit of mass damping as well. However, some materials used for mass damping, such as self-adhesive vinyl floor tiles or bitumen-based products (similar to roofers tape etc) are not as good as reducing airborne noise but adds mass to thin case panels etc to stop case vibration noise.
My $0.02 anyway.