Originally Posted by cjl

The exact phrasing is actually that the planet must have cleared its orbit, which is specifically defined as being gravitationally dominant. By the definition of a trojan asteroid, Jupiter fits this definition. Earth is not exactly challenged for gravitational dominance of its orbit either, as nothing else anywhere near earth's orbital path is even in the same order of magnitude aside from the moon, which is orbiting Earth.

As for pluto and neptune, the resonance is why Neptune is considered dominant - it is in a stable, well established pattern in which Neptune is by far the gravitational superior.