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Hasbro,
Your average speed-shop dyno probably wouldn't be able to produce this graph. The 2009 VW graph is a little different from normal in that it appears to be an iso-efficiency plot of metric-unit (g/kW-hr) brake-specific fuel consumption plotted on axes of Brake Mean Effective Pressure vs. RPM. The Prius chart is same-unit BSFC plotted on Torque vs. RPM. Since BMEP and torque can be correlated for a given engine's design it's roughly equivalent.
Wheel or chassis dynos can't really give you this graph. They typically require you to be in one of the higher gears to prevent overloading their absorber (brake) which means you can't accurately evaluate the lower engine speeds. Getting the full data set would require an engine flywheel dyno. You would also have to measure real-time fuel consumption at steady-state operation. Chassis dynos don't do steady-state operation well (depending on absorber type) and typically can not load-down without induced tire slippage.
The graphs have nothing to do with each gear. The colored islands indicate areas of efficiency between the labeled boundaries. Think of it as a topographical map of elevation where the highest elevation peaks (lowest numbers) are the peaks of efficient operation. You are correct in that it appears the most efficient acceleration would be to run the engine from 2000-3000 RPM at about 80% load.
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