While this observation is somewhat anecdotal, I can sympathize with the sentiment. But the real reason that commenters on Hacker News might appear conceited or condescending is because they usually comment to disagree. If they do comment to express their agreement, they are encouraged to do so only when they have a non-trivial contribution to make. And this focus on a high signal-to-noise-ratio (even though it may consist of far more disagreement) on HN is not by happenstance, it is by design (achieved through guidelines, self-selection, and curation).
The comment thread on Google+ referred to by the OP, is largely an echo chamber of low-on-signal assent, with the odd nugget in the rough. And while this isn't a bad thing for a marketer trying to cultivate and engage a large audience, it would be toxic for Hacker News as a community.
While the most insightful commentary generally lies in a well reasoned, thoughtfully worded counterargument, it's always hard to deal with being judged or disagreed with; especially in public. This may be exacerbated when an argument is worded poorly (see http://www.paulgraham.com/disagree.html). Unfortunately, the odds of either happening on Hacker News, are far higher.
i will never understand how he managed to have gained some significance in the world.
But the vast majority of the comments weren't unpleasant and it's a little unfair to paint everybody as not having the same views publicly as they do 'anonymously'. How would he know? It seems that even without anonymity people can be fairly offensive... ;)
While I wasn't aware that this was about our allegiances, it's Robert Scoble's choice if he wishes to identify with Google+ over Hacker News. I just looked at the comments on Google+ and Facebook, and I'd say that the discussion on Hacker News was far more vibrant and reasoned -- but it was definitely slanted towards a 'hackers' world-view.
...anyway, I sure hope Scoble will pick up my phone calls. :(
The reason I like HN is that there are people here who will happily and readily call out bullshit when they see it, and even if they are wrong, the HN community can debate their opinion - seldom is someone flat out wrong, they will generally have some kernel of truth/value in what they say.
If you read the Google+ comments (which I did yesterday as well), there is very little 'high value' comments there. Between the pandering 'I agree with you Scoble' to 'I don't know what to do' comments, there is a lack of intellectual discussion about the topic.
Scoble wanted to call out how 'toxic' HN is, but all he's done is convince me further that HN is the place to go for smart discussion.