hahaha!!!
Stoner was adamantly against adding the forward assist onto his design, but the US military, in all their wisdom, insisted. The problem with the forward assist is two fold. One has been mentioned that forcing a round into the chamber is a bad idea. The second is that when using the forward assist, there are some who STRIKE the forward assist. It is meant to be pushed, not struck, and if done repeatedly, will cause the small fragile parts that make up the forward assist to break and render the firearm useless until an armourer can get to it.
I know of no of no other rifle with a device specifically made as a forward assist (other than the defunct MSAR) other than AR15 designed firearms. Using the bolt handle as a forward assist (ala AK47 or M14) to force a round in has been known to touch off the round, causing injury to the shooter.
As others have said, the forward assist is not a useful part of the AR15 design.