Fairly common on lower range PHEV's (not so much the Clarity and Volt).
The incentives (Federal and State), sometimes combined with cheap lease deals by manufacturers looking for ZEV credits, can mean a PHEV is substantially less than the non plug-in version. My niece had a Fusion Energi lease in CA for something like $135 a month (IIRC), and had nowhere to plug it in at home (apartment) or work. The standard hybrid Fusion would have been substantially more.
The Plug-in Prius (predecessor to the Prime) was sold primarily in CA and something like 80% of those polled said they got it solely because of the Car Pool sticker and never bothered to plug it in (all electric range on the EPA rating was 0-6 miles, and it could not reach freeway speeds in EV mode)
Many of the PHEV's designed for the Euro market have 10 - 15 miles of EV range or less (BMW, Mercedes, mini)
And that article contains some assumptions that have been proven untrue or based on questionable studies (the Emissions Analytics study ignored upstream CO2 for gas/diesel production and counted only tailpipe emissions - but compared it to electricity generation CO2 on BEV's).
And that old tired dog "the grid would collapse if everyone had an electric car".