Hi
First off, I obviously did not use any trainers for the test.
About your test, you said you did "my test", yet you switched the UAZ with a HMMWV (packed with armor). It is therefore not much of a surprise, that your hits directly at the armor have less effect, than the hits on the UAZ. While I won't take a stand as to whether the M107 does realistic damage as it is now or not, I will however prove, that these vehicles aren't "invulnerable" to M107 fire. I made the short video below using FRAPS, which sadly only allowed me 30 seconds of shooting, so I might have spent a bullet too much on the UAZ (as you can see from the video it takes a while before it blows up/catches fire). In the video I am first entering the vehicle to prove it's starting condition (full health), then I move on to the shooting. When it comes to the HMMWV, I admit it takes more than a couple bullets from the M107 to blow up - if fired directly at its armor. If however (as done in the video) fired, so that the bullet won't have to sink through the armor first, it can be done.
The game is obviously (as already stated) 100% vanilla - only patched up to version 1.02.58134.
http://www.youtube.com/watch?v=O8pWR8uJ4cw
(I don't know where the sound went, it was there before the upload - sorry)
On behalf of ArmA 2 being a "simulator" or not, I think it's - as has been mentioned before me - rather expected, that the game isn't 100% equal to real life, since the other simulators out there strifing to do so 1) take longer to develop and 2) focus on one vehicle (Falcon, Black Shark). Of course I would like to see ArmA 2 move further towards the realism barrier, but as of now I beleive there are more important things to fix. :)