Also, the Suomi had 9mm so that you could use pistol ammunition in them (that's what i've heard)
You could do the same with the PPSh as the pistol calibre in most Red army pistols in this time was 7,62mm (very unusual for a pistol I've heard) and this was the same bullet used in the PPSh. The Germans even reconfigured some of the PPSh's that they captured so they could fire the 9mm magazines made for the MP40, this spared them the difficulty of looting clips of the battlefield.

Anyway it is true that the AKs focus on durability does reduce it accuracy, but this is mostly because of increased recoil and it being heavy, when firing one shot in normal combat circumstances it shouldn't really matter much if you were armed with an M16 or an AK47, though the M16 generally is more accurate and it's also lighter, but what makes the AK47 great is it's simplicity, durability and general effectiveness. The AK-74 is basically (so I've heard) the AK-47 reconfigured to fire a different calibre (5,45mm similar to the NATO 5,65mm) though with some other configurations. Many of the newer AK variants, are not as simple as the original weapons and have not been put into heavy use yet because of this.