Re: whats the diffenence neck vs. bridge
Because most pickup buyers don't have a lot of technical knowledge about pickups, most pickup makers (Duncan included) will tell you which of their pickups are designed for the bridge position and which for the neck.
The rule of thumb is there are fewer turns of wire on neck position pickups because they don't need nearly as much 'power' as a bridge pickup does for the reasons given above by Modest Cargo. The bridge pickup is almost always stronger so it can magnify those tiny vibrations near the bridge to balance its output (loudness) with that of the neck pickup.
In vintage output pickups, there is less difference in the number of turns between neck and bridge models than with more modern sound pickups. In some cases, like Gibson's 57 Classics, there is no difference at all, they are interchangeable. The more modern, hot bridge pickups are often close to twice the DC resistance of modern or vintage neck pickups. Check out the Duncan Tone Chart and you can see these differences for yourself.
Then there is the choice magnet which also heavily influences how powerful a pickup is...