Charon which is right next to Pluto in the orbit had never been a planet. Pluto has more in common with Charon than other planets. The discussion of dwarf planets has more to do with other bodies further out than Neptune, called transneptunian objects. There's lots of rocks out there past Neptune that are rather similar to Pluto and Charon, but would never be actual planets, but they aren't just asteroids either. So Pluto and Charon joined the new clarification of dwarf planets because it makes more sense that way.