Its true that some of the later models of the gun didnt have select fire but... everything i have ever heard about this guy has basicly said that it had select fire most of the time. So at least some of the maps should have a select fire ppsh. Millions of these guns were made and most of them did have select fire it just dosnt make sence to have none of them in the game with select fire.
As far as being dropped and fireing alot of the sub machine guns from that time period had the exact same problem. It wasnt out of the norm for that stuff to happen with any of the sub machine guns that have been used in the game. Keep in mind sub machine guns were still a fairly new concept during world war 2 and they are nowhere near as safe to use as the modern stuff out now. when they were being made back then they were basicly happy just to have a working gun. you dont want to be throwing a gun around anyway.
That being said it would be amusing to have one of these things go off every now and then when they get shot out of your hand. Would be funny as hell to have a dropped smg wipe out a few random people near by.
The ppsh was also more accurate then the other smgs of the war not just because of the longer barral or the ammo it used but because of the design of the gun the way the barrel shroud was longer then the barrel itself. it worked at a break and a compensator to control the recoil. so the gas beng expelled at the end of the barral was also helping to push the gun back down to where you orginaly had it.
If anyone is looking for more info on the ppsh or basicly any gun.
http://world.guns.ru is a good site to check out.