But the description of hold effects is different from the description of paralysis effects, iirc. Also, hold effects are mind-affecting, while paralysis (typically, anyhow- there might be exceptions) aren't. The two effects are qualitatively different.
I'd also say that something immune to poison would be immune to any poison, regardless of its effect- whether it inflicts paralysis, blindness, strength damage, con damage or whatever. Likewise, something immune to petrification is immune to it regardless of where it comes from.
Also not trying to be argumentative- just trying to explain my reasoning! And I could be wrong- idhmbifom.