The IAU hasn't actually defined "clearing the neighborhood"
Without having a firm definition of what that means, it makes defining a planet rather difficult. However, it's quite clear that they don't literally mean that the entire orbit is 100% clear, or it would eliminate Earth, Mars, Jupiter, and Neptune, since they all have asteroids in their orbits, in addition to Pluto being in Neptune's orbit.
Several years before the IAU came up with this definition of a planet, Alan Stern and Harold Levison proposed a definition for planets that included sub-classifications of uber- (heh, this forum erases the umlaut-u for some reason) and unterplanets, that also used the "cleared the neighborhood" language. Here's how they defined what they meant by this phrase: "Nearby small bodies are on unstable, transient orbits, or are locked in mean motion resonances or in satellite orbits." This definition basically means that an object that is the DOMINANT object in its orbit is considered to have cleared its neighborhood, which would exclude Pluto (because it's locked into resonance by Neptune), but not Neptune, Mars, or Jupiter (because they all lock their neighbors in resonance, not the other way around), or Earth (because the NEOs are transient).
It seems reasonable that the IAU is using the phrase in the same way that Stern and Levison did in their proposal, and is consistent with the IAU specifically listing out the eight planets.
