Here are the gas mileage numbers people have posted for the Prius:
Real-world Toyota Prius gas mileage
Non-members see only five results per powertrain. I logged in and filtered results for "ultra-light foot." Looks like about 52 MPG if you're easy on the gas, though radical hypermiling techniques might bump this to the 70 you mention.
Ran the same filter for the Z--only two results with an "ultra-light foot" for all model years, both for a 2003. One 100% highway tank good for 33.3, one suburban tank that yielded 24.5. So it seems that very few Z drivers are keeping their foot out of the throttle.