Everything has it bounds though. There is a point where a comment goes from well thought out and detailed commentary and into the realm of long winded rambling nonsense or expository blowhardedness. It should probably be just long enough to make your point.
There's something to be said for being able to communicate clearly and succinctly.
I do see pg's reasoning here, but I don't necessarily know that I agree 100%. Yes, it's true that longer comments are likely to have more thought put into them. And that shorter comments are likely to have less thought put into them. However, I oftentimes find that making my comments brief takes more thought than writing a long comment.
There was a post on HN a few months ago suggesting that comment length correlates positively with comment quality.