I think the speed difference has been explained well in this thread, with the most important causes being rider position and tire rolling resistance. Bicycle weight becomes a factor only on relatively steep climbs, and then only in proportion to the combined weight of rider, bicycle, and cargo.

Given the same tires on both, a high-end old school 32- or 36-spoke wheelset can actually have lighter rims, and therefore lower moment of inertia for better acceleration, than a modern one with a reduced spoke count. The sole benefit of today's fashionably low spoke counts is air turbulence, a drag contributor important in a fast race where seconds count, but probably not worth the reduced reliability for the average bicyclist.

For the record, the nearest thing I have to a high-performance road bike is a 10kg Bianchi with 32-spoke wheels and 100PSI Continental tires with a callout width of 28mm, but actual width more like 25-26mm / 1 inch. (True 28s, such as Specialized Armadillos, would not fit in my frame.)