It is primarily to avoid singularities, as I understand it. Paint robots prioritize long, smooth, constant-velocity plans much more than most industrial robots, as opposed to strength and speed.
The paint-style wrist (I've never heard the technical term for this type of wrist), as I understand it, is slower, weaker, and more mechanically complex (and as such, more prone to wear and/or mechanical failure) than the "normal" triple-roll wrists.
One other advantage the "paint" wrists have is that they can be completely hollow through the center, which some robots (Reis laser-welding robots are one example, IIRC) make use of to avoid running complex hose/cable bundles down the outside of the arm.
i am struggling now but 120-degree - yes, is in my mind confirmed from P200 hardware rj3 beyond, the wrist was 120-degree - and if i recall correctly, a 100 degree wrist on earlier paint models (P-150? until some point it also took the 120-deg? not sure, i think it may have been also an option), i might be able to confirm later
i'm not sure paint robot programming prioritises long, smooth and constant paths above any other applications, so I can't agree on that.
