Coincidentally, I happened to pick up an issue of "Psychology Today" while in line at the store tonight. Most of the magazine disappointingly turned out to be completely un-cited guesswork and bunkum, but it did have a headline article that applies exactly to this situation.
They claim that in human behavior, other people can be better judges of certain traits related to behavior -- like whether we come across as friendly, aloof, curt, etc. -- but the individual is more aware of things like motivations than anyone else can be. In any situation where an individual is unaware of their motivations, the best that anyone else can do is make wild guesses. The article called these "dark areas".
I can't say whether there's any actual support in research for the content of that article, but it does agree with most of the other pop-psychology garbage I've read, like "Blink".
Regardless, you and I have absolutely zero information about other people when it comes to guessing their motivations. We don't know their backgrounds, and we usually don't know them well enough to understand their personality. We certainly don't know an entire class of people well enough to tell them what their motivations are.
The best we can do is conclude that their stated motivations don't make sense given some other information about them.
Not to put too fine a point on it, but using yours and pg's justifications for this, I could tell you right now that you're defending pg out of a hidden desire to win recognition from him, since he has influence and resources. (If I were an actual real-life psychologist, I would probably also trot out some lame garbage incorporating "evolutionary psychology", and would conclude that you're behaving this way because ancient peoples who behaved this way had some kind of evolutionary advantage in the imaginary environment I've invented for them.)
You would probably object to that, and then I would grin and say, "Ah, but you don't understand your motivations as well as I do! If only you were more honest in your self-observation, you would see that I was right."
So, yes, while I agree that in some cases the stated motivations don't make sense, I disagree that we can assume that we know what the actual motivations really are -- especially without a shred of supporting evidence.
Hell, why not assume that Arrington draws fire because he's the founder and figurehead for TechCrunch, and people dislike TechCrunch because it sometimes picks on their buddies' startups? That conclusion has exactly as much supporting evidence as the one that pg drew. (None.)
Wait, I know! People actually dislike Arrington because he said he would debut a really awesome tablet PC by now, and where is it? We're all disappointed, and that's why we hate him. That conclusion, too, has exactly as much supporting evidence as yours or pg's. (...None.)
I don't dislike Arrington individually, and I don't even have a very strong opinion of TechCrunch, so I can't explain any motivation for actual hatred on my part. But, I also shouldn't think that I can explain any actual hatred on anyone else's part.