It is the way the trigger works and finger placement on the trigger. Because of the short web-to-trigger relationship most people will push or pull the trigger to either the left or right as they fire. We are taught early on to put the pad of our finger on the trigger and pull straight back. This action causes too much leverage as the finger curls so shortening that relationship to the first joint will help the mechanics of pulling straight back and ensures that the gun is less likely to be pushed right or left.
The most enduring feature of the Glock is the very short web-to-barrel relationship. As you hold the gun notice how close the top of your hand is to the barrel, there is no other gun with as close of a relationship. The XD and MP are close but not quite as close. This gives the shooter better muzzle flip control as the gun has less leverage in the hand.
Don't get me wrong, the Glock and the other copycats will never be precise target guns but once you understand the principles of the mechanics the bullet placement will be greatly enhanced.
They are great 'Beaters' and can withstand a lot of abuse and will operate no matter how many dust bunnies or neglect they are given while they lay in wait for action.
Personally, I prefer the M&P because of the fit and feel of the grip.