The seven movies in the Harry Potter franchise had to be very detailed, because the books were, and you can't disappoint the millions of children who learned to love reading from the Harry Potter books. Also, the producers were pretty sure that more than one movie would be made, so sets and props could be re-used. Might as well make them to last, and not skimp on the quality.
What came from those basic ideas was a sumptuous, detail-oriented set of films that we are always learning more about. You'll learn a lot from an illustrated list of 70 Intricate Details About the Harry Potter Movies at TVOM.