>I see no hard observational data or case study
references for the famous claim that "trapped moisture rots the underlying
wood".>

Christopher - I've never seen any scientific studies re this, either, but
have many times seen the result of rain water blowing in through J-beads, and
breaching dried-out and/or pulled-apart caulk joints at windows, doors and
cornices.  Fifteen years is all it can take to rot wooden sills.   Fact is,
insects and water can always find a million places to enter the siding, and
the damage they cause is always hidden from view under the guise of a
periodically-examined and well-maintained exterior.

John Mascaro