I agree with this, especially since a lot of people will interpret politeness as being a sign that your decision is negotiable.
That polite "No, because of X, Y, and Z" rapidly turns into "I have made up my mind, no" and then into "This is not a fucking debate, so no, and fuck you." very quickly, especially if you're dealing with a constant deluge of stupid requests.
I'm not going to judge Linus for his outbursts, as obviously his method seems to work pretty well.
Politely saying no takes time and effort, especially if communication isn't your strong point. If I'm walking down the street, I'll probably be pretty polite to the first homeless guy that asks me for a dollar. By the time the hundredth flags me down before I'm even halfway to my destination, I'll have boiled that initial polite response down to "Fuck off."