It seems to me that the 'media' seems to making this some sort of benchmark, as if METPOL helo's are some form of air gods and if they don't fly no one else should.
My general but limited knowledge of police helo work is generally in response to operational needs i.e. chasing the bad guys, and if vis is low and operating in a more 'random' fashion across built up areas as opposed to flying heli routes would make their decision making process very different from normal commercial ops wouldn't it?
The MET are
AFAIK the only Police helicopter unit that patrols, that is they take off and loiter waiting to be called, or listen to the ground radio traffic and offer to assist in situations where they think they could help.
I flew with them one evening, back when they still had the 222s, and we took off and spent the first twenty minutes bimbling around waiting for something to happen.
But I would imagine that their criteria is different to most traffic. Seeing the ground is what they do, so they may well have grounded themselves far sooner than called for for purely safety reasons.