True, although the Prius is more of a Hybrid-Hybrid: At low speeds it is a series hybrid with the majority of the engine power going to a generator and then to the motor driving the wheels with only a small amount directly from engine to wheels.
At high speeds the situation is reversed and it acts more like a parallel hybrid with a large fraction, up to 100% of engine power, going straight to the wheels.
This is done to maximize efficiency since the mechanical transmission has an efficiency of 95% or more but the electrical losses through two motor/generators are about 20%.
As you say the parallel approach also avoids the need to size the electrical equipment large enough for the full load - the generator is only 30KW even though the engine can output close to 60kW. The motor driving the wheels is 50kW as an additional 20KW can come from the battery.
kevin