How would you like me to politely word he's wrong?
Since you've been so polite I'll just state the facts.
The tech specs of the drive don't take into account that most people will have their hdd inside an enclosed PC case, which blocks some noise.
They certainly don't take into account the fact that my drive makes no direct contact with said case (in fact it's held securely in one of the 3.5" bays with bungee cord).
As has been said, they also don't account for the fact that most users, even most "quiet PC" users, will have at least two low-rpm fans. Mine are either controlled by SpeedFan or fed 7V instead of 12V.
Now I'm a fan of "quiet PCs" but I do everything with an eye on my bank balance. Hence you won't find me buying £150 fanless PSU, a £50 heatsink or indeed a £200 SSD.
However the bungee cord and fittings cost me about £4, SpeedFan cost me nothing, the quiet fans I have cost about £10 each, and I have a quiet SeaSonic-built PSU and a quiet Gigabyte GTX460.
In that setup, there would be no benefit -- no drop in noise levels -- if I switched out the WD green for an SSD.
And when I turn my machine on (it's under my desk btw), most people will say "is it on?" because they don't hear it. It does make a noise (not a harsh or irritating noise), but it's so quiet as to be acceptable to all but the most noise sensitive people.
So there you have it... for everyone who doesn't need actual silence, an SSD is not essential for the purpose of having a quiet PC.