Mon L wrote:
These books aren't thinner or lighter than the other omnis.

From DrDoombot's post:
 
Lee/Kirby Cap:  840pp, 2.5 kg
Michelinie Iron Man:  906pp, 2.4 kg

The book that is 66 pages smaller weighs about 3.5 oz more.  Not a huge difference, but not zero. 
 
Doesn't matter so much to me, though, as I am not one of those pantywaist milksops who complains that Omni are too heavy.