I agree that it is not needed on a PHEV and I probably wouldn't purchase that option on a PHEV. However, there are at least two PHEVs on the market now that support DC fast charge. The BMW i3 Rex and the Mitsubishi Outlander PHEV.The Volt does not need supercharger technology. The Volt has a range extender engine that eliminates the need for rapid charging on long trips.
Supercharger technology is appropriate for BEV's but not needed for EREV's.