Detecting Under the Microscope: The PAS Plough Damage Argument

In his 1210 talk Outreach or enforcement: lessons learnt through the Portable Antiquities Scheme   to the Newcastle Conference, I see Michael Lewis trotted out the well-worn argument:

[SLIDE 12] It is important to bear in mind that most finds recorded with the PAS (92% in 2007) are recovered from cultivated land and therefore vulnerable to agricultural damage. Archaeologists once thought that such finds, out of (immediate) context, and in the plough-soil, were of limited archaeological value, but metal-detecting has transformed that view. 

Well, first of all, I wonder where Dr Lewis gets the idea that archaeologists "once" dismissed the evidence held in ploughsoil to be gained by systematic surface surveys. Not for a long time have they, it has been a standard investigative technique for coming up to half a century (I once contributed an extensive bibliography to the PAS Forum on that topic, but it has disappeared when the Forum was closed, it would seem that while it was up, Dr Lewis did not see it). Anyhow, the slide illustrating "most finds... vulnerable to agricultural damage" is the Ringlemere cup, a gold beaker, bashed by something at some time in the past. Whether or not that is a modern tractor-drawn plough is hard to say. What however does seem clear is that it had been in the body of the Ringlemere Barrow, the levelling of which was responsible for exposing it to damage. So is this the best example the PAS can come up with after fifteen years of receiving dug-up finds from artefact hunting "partners" to prove the anti-conservation thesis "Better Out Than In?".