IOW, it's just some semantic rephrasing by Lehner, and in the case of Hawass -- "The pyramids were probably not built by slaves because slave labour was not widely used in Egypt at the time" -- just denial, followed by the use of the denial as evidence that the denial has a basis in evidence. :') It was slave labor. The Nile flood, coupled with agricultural techniques adapted to the conditions, made large agricultural surpluses available, leading to literacy, arts, and of course monumental works of construction for the aggrandizement of the god-king. A peasant in the society would have been much better pleased to keep the fruits of his labor, and enjoy the leisure time made possible by his industry. Not that I'm a Marxist of course. :')
Doggone it, I was trying so hard not to quote Hawass. The "...slave labour was not widely used in Egypt at the time..." should have been a clue. I thought the phrasing sounded familiar. I should have checked it further.
I don't think that it was just semantic rephrasing by Lehner. The labor was compulsory, but it was paid. It's not a whole lot different from mandatory military service like modern-day Israel, except that it was a whole lot more than a two-year hitch. Kind of like permanent, part-time, mandatory physical labor.
Don't get me wrong: I don't approve of mandatory labor, paid or otherwise. Far from it. However, it doesn't really equate to slavery. I'm not aware of any records of peasant farmers being bought and sold like commodities, for example. Another example would be punishment. There was whipping as punishment in the early US Navy, and confinement with only bread and water up until just a few years ago. That doesn't mean that US sailors were slaves.
I don't think that it was merely semantics. He was making what I see as a valid distinction between slavery and mandatory service. What about the military draft? Is that slavery because the service is mandatory? I don't see that it is, and I believe that is the point that Lehner was trying to make.