Wed 22-Feb-12 01:35 AM | edited Wed 22-Feb-12 01:37 AM by PerroneFord
This is like asking about carburetor on a modern racing car. Photosite size IS a significant factor of light gathering ASSUMING the underlying technology is the same. Well, technology has moved on considerably since your D2HS was new.
The light gathering of the 36MP D800 is about 4 times as good as your D2HS, regardless of the photosite size.
Thom Hogan's book, as excellent as it may be, is a guide. Not the definitive work on the subject.