http://news.bbc.co.uk/2/hi/world/europe/10440300.stm
There's really no logical reason for the workers to dress in 13th ce clothing as they build this castle. What they wear doesn't affect the construction of the building. It does, however, add "soul" to their efforts.
By living the experiment to the smallest, insignificant detail, they are making it a reality.
I like that.