why not the worms and the rain will take most of it down and the nuterants are going no were untill your plants use them, or dig it in in the spring as far as I can see it six of one and half a dozen of the other.

Either, really - I don't know how cold your winters get there, but over here, if you have heavy soil, it makes sense to dig it over and leave it in clods, adding manure as you go, because the frost will break the clay down. If your ground freezes regularly in winter there, I'm not sure putting manure on the top now will be of much use - worm activity (which is what takes it into the soil) will be non existent if the ground is frozen, so it might make more sense to wait till spring and then dig it in, or dig it in now.

You 'should' be okay just putting the rotted manure on the surface, just dig everything in come spring before you plant. The only caveat I would have is that you should not put on frozen ground or ground that is likely to freeze within a couple of weeks of the manure being put down (at least not for more than say a day). Used as a top dressing the manure will rot down no matter what BUT if the soil is frozen then the nutrients can not possibly go into the ground and will simply run off. If you are concerned spread the manure and then fork in lightly, this will ensure that everything ends up in the soil not the local water course! Which is bad for the environment :-)