Not forgetting, of course, the extra set of buffer stages between pre-pwr to cope with impedance mismatches.  Of course, integrateds dispense with the buffers so there are fewer components (and less cost!) in the signal path...

I don't think that stumblin's point about greater component value in an integrated is particularly apposite.  Equipment is sold on a fairly constant margin, and as a result, it's unlikely that a 4K amp will have 2K of parts if pre-pwr or 3K of parts if integrated.  He's right though (and michael picked up on this) that some of that parts cost will be in elements which contribute less directly to the sound of the amp.

reg