(I hold the position i do precisely because it's backed by research, not just my own random thoughts and experiences)
It's probably not that being an asshole is good. It's that if you are a genius/visionary and nice, your genius gets diluted by the people around you. Let's build a genius/asshole map:
1. Genius, non-asshole: You start a genius-level thing, it is brilliant and awesome. As it progresses, less brilliant people get involved. They start wanting power and influence. You know that the things they want to do kind of suck, but you're too nice to tell them that. Over time, they ascend to positions of power, because you, out of niceness, allow them to, and your thing descends into mediocrity.
2. Non-genius, asshole: You're just mean to everyone. If you start any sort of thing at all, it goes nowhere, because it's not very good, and nobody wants to work with you.
3. Non-genius, non-asshole: You're nice, but so are lots of people. This goes nowhere.
4. Genius, asshole: You start a brilliant thing, because you're brilliant. You're mean to people who deliver anything but the absolute best results. So who stays with you? People who always deliver the best results, or, alternatively, people so enamored with your genius or the thing you've created that they're willing to tolerate it. Congratulations, you've managed to filter your underlings to only the best and most passionate people - you have a high probability of achieving something great.
Note that this is not an endorsement of this behavior. Just an attempt at explaining why it is that these types of personalities seem so common among highly successful people.
However, what about a genious which politely replies something along the lines of "I'm very sorry but I don't think your contribution aligns with the goals and/or philosophy of this project.". That is not a nice nor an asshole response. After reading Linus' text, it seems to me he intends to get somewhere near this point.
I agree that, in principle, someone could do that. But I think in practice the people who can stand firm in that response, while remaining polite over many years, are pretty unusual.
Do you really think you can provide that kind of consistent response to different types of people? Your reply is most of the time dependent on the people you are interacting. It is very easy to draw a nice person to a fight or being rude. It is very hard to analyze because the scenario sample space is infinite.
I think that now, today, Linus could afford to be less of an asshole. But I honestly wonder if the project would've have succeeded so well without him being so strict and demanding in the beginning.
EDIT: Yes, I think that it is possible to be strict and demanding without doing ad-hominem attacks and without swearing. It's just that it's very rare.
As someone once said, "If the person who made your computer wasn't an asshole, it probably wouldn't even turn on."
Obviously, that quote is utter hogwash, but it might be worth saying explicitly, at least for HN culture: cooperation is essential, and would you cooperate with an asshole?