I really do try (stop laughing!) to explain why when I comment - but only if the remark made suggests that the speaker will understand what I'm saying.
Example:
Q: "Should I run a 6" rod in my 302 SBF?"
A: "No, not enough deck height to allow a piston with any stroke you would use", but the question is serious - he just hasn't done the math
Example of a remark where I would make only a short response:
Q: "Should I run an 8" rod in my 302 SBF??"
A: "No" - he has no idea what this is, he's just recycling data from somewhere else
There is also, in my opinion, a significant difference between these caveats:
IIRC means it's believed to be true (not my opinion), but I can't place it
AFAIK is a bit weaker
IMHO is more subjective
"2 + 3 = 5" is not an opinion, whether you agree with it or not, and we all have our own favorites.