Plug in ignores one very large population: people who live in apartments. Unless the apartment builders start to consider charging stations sufficient to the population, plug-ins are pointless. A hybrid works since I don't need a plug.
And it's really not that hard to add charging infrastructure to apartment parking. It's just a matter of will. The technology is simple and relatively cheap.
You'll start to see companies offer owner of apartment complexes a pretty good deal: they'll install the chargers for free in exchange for them charging the tenants for the electricity (+ margins)
This is a problem that be market is pretty good at solving if the government just gives its kick-start. Once plugins hits 20-30% market share (sales) it'll practically solve itself.