I think Second Phoneix is overstating things a bit, but it does seem to be increasingly the case that police forces have policies that avoid officers taking any chances with suspects with anything that could possibly be considered a weapon. They are discouraging them from trying to engage by talking to them, or even things like wrestling the weapon away, when it would be safe to do so.
It seems to be about responsibility and liability. There is the issue of people being sued. There are also insurance considerations. If an officer is hurt, and he took "unnecessary" risks, insurance and workers comp could become problems. The employer is not going to want to allow that to happen, so they put in place these stupid, strict policies.
As an example of how silly this is: my husband a year or so ago went to a demonstration for work involving bullet-proof vests. Here, the police are all required to wear them as part of their worker-safety rules. What the company representative told them though, was that in our province, this was a silly rue. In most situations police here are exposed to, gun-fire will go right through the vests. In that situation, they actually cause serious problems, because fibers from the vests go into the would and cause all sorts of trouble.
But, the insurance people like to see that something is being done, even if it is something stupid.