> I interpret that to mean someone purchasing a home today must have roughly twice the resources to purchase the same home as someone in the past

Case-Shiller is not adjusted for inflation. In addition, it does not take into account interest rates. Until recently, mortgage rates were extremely low. It takes less resources to pay the mortgage on a $1,000,000 house at 3% interest than it does to pay the mortgage on a $250,000 home at 19% interest (which is where interest rates topped out at in the 1980's).