That was my whole point - just to provide some information on the thread. Nothing more.
Agreed that a .22 out of a carbine is pretty quiet outdoors; however, try shooting a pistol .22 indoors or even outdoors without hearing protection - pretty loud. Within a few feet of the pistol, you'll get a db reading of well over 140, and since the db scale is logarithmic, and every 3db increase equates to the sound being half again as loud, that's quite a racket. With a good can attached (and most modern ones are really good), it's as quiet, if not more so, than an air pistol, and a lot more powerful and capable.
There's a whole bunch of good info available on this topic. Best book is Al Paulson's "Silencer - History and Performance." Both Volumes 1 and 2 are a treasure trove of info on this topic. You don't need to be an engineer to understand it all (although I am), but it does read a bit more on the intellectual side than the latest from Clancy, for example.
As for the $200 tax, agreed we shouldn't have to pay it, but that's equal to a decent dinner with the wife, and while I love her dearly, I'll gladly skip a few to have toys like this.
And with regards to commonality of calibers that are suppressed, there are by far more .22 cans out there than any other caliber simply due to cost and usefulness. Most 9mm fodder is supersonic, so you still get the ballistic crack from the weapon. That's why something like the HK MP5SD is being phased out, since it is heavily ported to keep the rounds sub-sonic. Great for sound performance, but lousy for ballistic performance.
.45 ACP is a much better (but much harder) round for suppression, since it can stay subsonic yet remain very effective. Most 9mm ammo must be above 1,200 fps to ensure proper expansion, and once you get past 1,100 fps, you run into that ballistic crack issue again.
But don't believe me (hell, I don't care one way or the other quite frankly). Read and learn from the people who work with this stuff on a daily basis - Paulson, Engel, Dater, et. al.