Well in my opnion the reason why wings drop has got nothing to do with the most of the discussion its pure and simple pilot error. Most pilots have to go and annoy the poor aircraft and upset it.
When I first started instructing in tommys I had a wing drop every time. A year and a bit later and 900 hours they didn't drop a wing. Same airframes. So I can only conclude it was me being cack handed or cack footed. Give it to the students and it used to drop a wing again (much to thier disgust).
And yes crash one a kick up the arse is required. Its all to do with flow over the aerofoil and when the boundary layer becomes unstuck. Although I would slightly disagree with the turbulence comments because sometimes the engineers induce it with vortex generators because it delays the boundary layer becoming unstuck.
The best way to have a play with this is take a piece of card and get some one to drive down the road and have a feel of the forces required to hold it at various angles to the airflow sticking it out the window. If you can get hold of an aerofoil profile even better. As you go from flat lifting the front edge and droppping the rear you will feel an upwards force and a small rearward and when you go too far it will disappear and be replaced by a relatively large force in the opersite direction to the direction of travel. Once you lower the front again it will go back to an up force with a bit of rearward force.
Go have a play with it, its much more intuative if you can see and feel whats going on.