Well, they were already 'minor planets', when planet had the fuzzy definition of any body that orbited a star (i.e. anything in our solar system that wasn't the Sun or a moon).sprunkner wrote:The real reason is that if one makes Pluto a planet, one must pretty much make every icy object at the end of the solar system a planet. It's a matter of not making exceptions.
If you look at the larger picture of the Solar System, there's 3 major regions:
The Ecliptic - where all but Pluto reside,
The Kuiper Belt - where Pluto, and all the dwarf planets bar Ceres reside,
The Oort Cloud - where comets reside.
The shape of these three regions is also distinct:
The Ecliptic is a thin disc-shaped region in the same plane as the Sun's equator,
The Kuiper Belt is a much thicker region, thickening as it moves outwards,
The Oort Cloud is a spherical region extending until the edge of the Solar System.
The shapes of these regions are defined by the orbits of their constituents, which in turn are governed by their distances from the Sun.
http://en.wikipedia.org/wiki/Solar_system