which in turn seems to be based on IRS aggregate taxpayer data. Based on a quick of the IRS data referenced, the "effective rates" does seem to be actual effective rates (ie. calculated based on how much the IRS is getting, rather than calculating based on what the brackets are). That said, I can think of multiple reasons why they don't correspond to the graph above:
1. At least in the early data, millionaires don't make up that much of overall tax take. For instance in 1945 they only made up of 0.1% of overall tax receipts. That means the effective rate of 64% makes a negligible contribution to the effective tax rate of the entire economy as a whole.
2. The threshold for millionaires is also not adjusted for inflation, so you'd expect the effective tax rate to drop as the brackets are moved up to account for inflation.