It is a legitimate firing position. I have been trained in it, and have trained others. It generally seems to be be more stable than a hasty kneel and works pretty well. Some of my older compatriot with knee problems can't do it, though. H&K teaches it. It is slow to move out of, but it is good for accuracy at intermediate ranges.
Bin Laden showed very poor executuion of it though, and showed poor training and safety.
What is up with the AK he was shooting? It had and old-style AKS-74 folding stock, an AKM muzzle brake, and apparently AK magazine. Was this a cobbled together AK? A Peshwar knock-off? Bin Laden usually appears with an AKSU-74 with a 40-rounder RPK-74 magazine. All in all, I'd say these guys are idiots when it comes to basic small arms skills. They probaly keep bayonets fixed to "make the bullets go straight" and set their elevation settings to the highest level to "make the bullets more powerful" like some African troops I heard about.