This morning, before heading to work, I was trying to explain to Bronwyn why 5th harmonics are hard to sound on the neck pickup. I think I explained very poorly, so here is a better explanation, with crappy photos.
The first photo illustrates an open string with no harmonics. Note that the string vibrates the most at the 12th fret. In this case, more vibration is picked up by the neck pickup than by the bridge pickup (the photo is of an Ibanez S520 EX – a beautiful guitar to play – and extremely heavy!)
In this second image, the string is struck with the finger resting lightly against the 12th fret. This has the result that the string’s vibration is cut in half, with two waves on the string instead of one. Note that there is little-to-no vibration at the 12th fret. Again, the neck pickup picks up the most vibration.
In this third image, the finger rests against the 5th fret, cutting the string into four waves. Note that there is no vibration at around the 25th/26th fret, which coincides with the neck pickup. That means that if you have your neck selector set as your only pickup, then you will not get much sound at all – especially on a telecaster or stratocaster, which seems to coincide exactly with that point.