"But it remains as a fact that previous no fly zones began their life as reactive and the Arab League could well have genuinely believed that that is what would happen with this one."
It's worth a quick look at the history of the Southern no fly zone in Iraq.
www.globalsecurity.org/military/ops/southern_watch-1992.htm
It began in August 1992.
Nothing seems to happen until December 1992 when the Iraqi's try to fly a plane over it and it's shot down.
In January 1993 the US and UK tell Iraq to remove it's missile sites from Southern Iraq, we know where they are but haven't attacked them.
Later in January a punitive strike is made against some, but not all, of the missile sites more in reaction to other aggression by Iraq than to do with the enforcement of the no fly zone. And then after that any other SAM sites that lock onto a western aircraft are dealt with.
So the SAM sites were there and were known about. Some, not all, were attacked following their non-removal and other events. Other sites were then only attacked when they interfered with allied aircraft.
The sites were not just attacked at the commencement of the no fly zone, which is what is happening in Libya.
Don't get me wrong, I'm not saying that what is happening in Libya is wrong but I am saying it is unusual and perhaps what some did not expect to happen based upon past events. It might also have caught Gadaffi by surprise who could well have though he could get away with a lot more than he has as long as he didn't target western aircraft or fly anything.