Hmmm - isn't the point that Stonehenge was most likely built to serve some purpose over a fairly long timescale (and not just for the purpose of amusing future archeologists!), therefore the question is not so much "how was it built" but "how it was used". Considering some of the much simpler solstice-marking devices that were built at different locations within Britain, Occam's razor would suggests it was for more than just looking at the sunrise on one or two days each year. But we don't have the user manual any more.
Like I said, once you've built it (whether for long or short term use) you don't need that specific knowledge again unless you plan on repeating it. The use of something has little to do with the knowledge required to build it, if any.
The 'architect' and constructors of stone henge may have been the only ones with the knowledge how to do so. Once they die, that knowledge is gone. Many people may have known about it's use so it remains. However, uses evolve over time and so information is subject to change with it.
Actually, the reverse is not true. Stone inscriptions and paper records have survived for centuries and even millenia. Much information about the 20th century history of computing is already irretrievably lost, either because it was only stored on materials with a short life, or because there is no longer any technology to read it, or even to read the instructions for re-creating the technology.
The fact is that in 2011, we have a far more complete knowledge of the thought processes of Leonardo da Vinci, Galileo, Newton, etc, from their surviving writings, than we do about the early pioneers of electronic computing. This does not necessarily seem like "progress" to me.
Well that all comes down to what you consider the progress to be. You pick a very specific example, but the fact is we only have records from the past of very specific people. There is little recorded about joe blogs down the road and his random experiments in his garden shed. But now, you only have to be in the internet and you could find all about it.
My point being, we have a lot of information stored now about a multitude of things, where as previously there was only a few records from rather specific subjects.
