Atkinson claims to have measured data which proves this. Apparently it is to do with higher RPMs resulting in lower internal cylinder pressure.
That, in itself, does not prove greater wear. I'm surprised that Atkinson makes that claim (I haven't seen the seminar material so I can't say if he does or doesn't) as it isn't really in keeping with what I know of the Deakin-Braly teaching on engine management.
I can well imagine that lower RPMs at high power setting can increase the cylinder pressure to a dangerous level, but I can't believe that the wear vs pressure relationship is linear enough to mean that this would extend to lower powers in a way that dominates the effect of engine revolutions.