Hi Thanos,
RE your first question. The words "large construction projects" are your own, not mine. Accelerating activity here refers to the whole social machine that was the Old Kingdom. In the first chapter and the introductory part of that chapter in particular I wanted to convey how the pyramids are just the tip of a social system founded in industrial scale agriculture and grain distribution, so the 'activity' here does not just refer to monuments or pyramids. There were other structures such as dams and canals being constructed at that time, some of which were necessary for the construction of the pyramids.
RE your second question, If you read the whole paragraph where I reference Hornung, I specifically noted that the dates for the Old Kingdom are expected to be revised based on the latest information published by Ramsay et al. in Science 428 (2010) p 1556, so that Hornung and Shaw are probably both incorrect for the Old Kingdom. In that case it does not really matter which is used, as long as the reference is included for the reader. For the Middle and New Kingdoms the dates are more secure, and are included for general information only, for novice readers.