Unless its a military controlled no fly zone, which is enforced by an air force, its quite normal. Commercial jets fly too high and too fast to be hit by anything other than very sophisticated and expensive weapon systems.
If that's the airlines' reckoning, then I reckon they've just been proven wrong about the risk of going into this and other such areas.
All the airliners were doing it, according to reports. It's a route which saves time and presumably money. At the end of the day its the fault of the people who were responsible, no one else.
Because, as we all know, war fighting follows strict rules and fighting men are always sober and careful of who and what they are shooting at. /sarcasm
Hopefully a good sized lawsuit is coming from the bereaved and the airlines will learn not to endanger their passengers to save some time and fuel.
And just because everyone else is doing something, doesn't mean it's the smart thing to do.