I think I disagree with your comment regarding programmers: Linus is admired for such strong opinions, close to impoliteness, for example.
More than a jujutsu technique for dealing with such incisive questions, it is clear that being the second contender to enter the marker saves you the trouble of having to create such market (and it is sometimes reasonable to play it this safe). It's just a different approach to making money. To me, a VC asking this is a sign of weakness on his behalf (due to ignorance?).
1. Linus is in a dominant position. Dominance doesn't invoke indignance when it's directed toward non-tribesman or by the alpha (the paper discusses this). What's interesting about this, is you can read whether someone perceives Linus to be an/the alpha based on whether they reject or accept his behavior. Further interesting, if they accept his behavior, they are likely self-associating with whichever tribe they consider Linus to be the alpha of (e.g., programmers, Linux, OSes, etc...).
2. Yes, I agree on a VC's concern of risks on the viability of a market. (See First Mover Advantage myth) I'm focusing more on the way it's communicated rather than the content or the why.
3. Yes, I think you're right that a VC is masking weakness if he asks this, as opposed to, "How are you different from X?" Though, IMO it's still an assertion of dominance, similar to a veil of bravado.
More than a jujutsu technique for dealing with such incisive questions, it is clear that being the second contender to enter the marker saves you the trouble of having to create such market (and it is sometimes reasonable to play it this safe). It's just a different approach to making money. To me, a VC asking this is a sign of weakness on his behalf (due to ignorance?).