Hi Paul, thanks for the comment. I think the IAU decision is making more and more sense over time. It's a shame that only a tiny number of astronomers actually got a chance to vote, but the decision is a good one, and ends the ongoing concern that larger and larger planets will be discovered past Pluto.
I am the person who wrote the comment you quoted above, and I believe there are genuine reasons to question the IAU's competence. The Pluto decision was made by 424 IAU members, who make up four percent of its total membership. The process by which the decision was made was flawed and highly political. The definition adopted was rushed through on the last day of the conference. Most of the astronomers who voted are not planetary scientists. No absentee or electronic voting was allowed. How much sense does this make for a science-based organization?
The vote reflects the view of dynamicists, whose primary concern is where celestial objects are, versus planetary scientists, who focus on what the individual objects are made of. Dr. Alan Stern, Principal Investigator of New Horizons, rightly said the IAU vote was "hijacked" by dynamicists with their own agendas. Watch the video of the IAU planet definition session and vote, which is on their web site. It's like watching theater of the absurd. Clearly this very flawed definition (a "dwarf planet" is not a planet at all)was railroaded through by a tiny minority. It was immediately rejected by over 300 professional astronomers led by Stern, who described the process and outcome as "sloppy science that would never pass peer review" and "an embarrassment to astronomy."
Pluto, Eris, and even Ceres are fundamentally different from the asteroids in the asteroid belt and the other objects in the Kuiper Belt in that they have achieved hydrostatic equilibrium, meaning they have enough self-gravity to have pulled themselves into a round shape. Their geological processes are much more akin to those of the planets than those of the asteroids. And if we apply the "clearing its orbit" requirement strictly, none of the other eight planets would qualify either.
What the IAU came up with is not a proper definition but a sham, and contrary to Fraser's comments, it is not making more and more sense over time. In fact, if we find a Mars-sized object in the Kuiper Belt, the definition will be all the more untenable because that object will not be considered a planet while the actual Mars in its current orbit is considered one.
If the solar system has 130 planets, so what? Students learn the Periodic Table of the Elements, and no one complains that we have to restrict the number of elements because there are too many to learn.
A good definition would keep "planet" as a broad category covering all non-self-luminous spheroidal objects orbiting stars (definition courtesy of my astronomy instructor Al Witzgall). We could then have multiple subcategories of planets such as terrestrial planets, gas giants, ice giants, and now, ice dwars, the last of which would include Pluto.
Like many, I have lost respect for the IAU because of the way they rushed this sloppy definition through. Why not wait until 2015 when New Horizons gets to Pluto and Dawn gets to Ceres to come up with any definition? At that time, we will learn more about both these bodies than we have ever known.
I am passionate about both astronomy and language, and I am far from being the only one who cares about how we classify solar system objects. The many voices objecting to Pluto's demotion should have made this obvious. Criticizing someone for being passionate about this sounds like little more than an ad hominem attack.