Crikey, mate (pronounced "moit"), there's nothing neutral about General American! But let's say, within the US, there is a somewhat-identifiable dialect that people are and have been moving towards for a while, which we can call the prestige dialect, which is adopted by newscasters. There seems to be a similar situation in England. I'm not sure about Canadian dialects, except that US General English is not neutral there. Maybe a reasonable test of "neutrality" would be to ask people, listening to a particular dialect, whether that person "talks like you"; then the more people that are thought to "talk like you", the more neutral that dialect is (if you can figure out how to devise the sample). General Canadian English would probably be more neutral to the US audience than the classical regional dialects (Southern, New York, Chicago, Boston). I don't know, though, whether General American would be judged as universally further away than, errh, Labrador English. I'm pretty sure that General American is as un-Australian to Australians as General Australian is to Americans.
I think one would be hard-pressed to say that there is a neutral dialect of Norwegian. There are the literary standards Nynorsk and Bokmål, but nobody actually speaks those languages (as far as I can tell), instead they speak whatever people in the area speak, and there isn't a huge social push for everyone to talk Oslo talk. Parisian French is favored in many parts of the world, and so on. Especially for very big national language, there tends to be a particular variant that is favored, though it may differ by country. (E.g. Swahili in Tanzania vs. Kenya; English in the US vs. GB; French in Canada vs. France).
The right concept to attach to that language form is not "neutrality", it is "prestige". However, the idea of "neutrality" does enter into the discussion, because people usually think that the prestige dialect is how the language should be, i.e. it is purest, and hasn't got a bunch of other stuff added in that corrupts it from its natural, neutral state. This is clearest, to me, when you consider clashing notions of neutrality / prestige in different nations.