REALLY Mick?   I have NEVER heard Page nor Clapton use this techinque.  Kindly dear sage, direct me to ONE song where Page uses a tap techinque (we're talking two hand tapping here, correct? not simply a hammer-on).  And Clapton???  Bullshit.  I don't think his mind would ever entertain the possibility that the Right hand can leave the pickguard.   He's been playing the same 3 notes for the past 20 years.  Played a few more with Cream. 

However...I have heard tell that it is/was a techinque used by some classical guitarists many eons before Eddie was even shitting in his diapers.  I don't know which ones, honestly.  The first I ever heard of it on electric, was certainly EVH, or did Stanley Jordan do it first???  Followed by Yngwie and now hordes of others.  

You just might be interested in Hans Tammen (Endangered Guitar).  See http://www.hanstammen.org.   Now...there's some interesting "technique".   I have the CD..takes a little courage to hear the whole thing in one sitting straight through. 

Gene