Depends. At most companies, how you handle a simple interview is still relevant if it's for a revenue generating or client facing role (e.g., sales, marketing, and project management).
Granted, most technical roles aren't generating revenue or in contact with clients, so this isn't nearly as important.
Wait, what? The products I build don't generate revenue for my employer?
This is one of the reasons sales and marketing often have a lot of power in modern business organizations (at least, as long as sales are good).
Someone who gives halting, but reasonably acceptable answers throughout an entire interview might be better at understanding technical problems than giving verbal answers in a pressured situation, and find the latter aspect far more difficult than the actual problem-set covered in the technical questions.
On the other hand, someone who confidently, thoroughly and unhesitatingly reels off answers to all manner of non-technical questions should, at least theoretically, be similarly comfortable talking about technical problems they don't find especially hard... And if they're excelling in the pat interview questions because they've done far more interviews than average than may also be a negative mark
[1]many of which, as others have pointed out, bring in a lot of revenue
But also, my experience in TAing the weed out course for the CS major (and from seeing my fellow TAs teach and work, who were more or less the best in class at my University--so much so that I was flown out by a company simply because of my involvement in that class) was that social skills had absolutely no correlation to technical ability: your ability to understand how pointers or complex data structures worked had absolutely no relation to how socially fluent you were. In fact, it often went the opposite way, up to a point: there was some base line of social fluency that everyone I worked with and the best people I taught seemed to meet. The single best coder I have /ever/ seen work (he alone makes me absolutely certain that the best people in our industry are 10x/100x more productive than the average) was also one of the most comfortable with people and had a very clear idea of his career goals. I'd expect him to give confident, unhesitating responses to "Where do you see yourself in 5 years?" and "What's your greatest strength/weakness?" Negatively weighting that would mean you'd miss the hands down most productive person I've ever seen work: and you'd probably miss a decent number of the other people I taught with. (Who, as I said, were basically the cream of the crop from the program I was in. Not all of the best people were there, but all of the people there were among the best.)
Now, I don't think they're particularly good interview questions, even though I understand why they're asked. I think that asking questions about actual workplace soft skills (conflict resolution, for instance) would be a much better use of everyone's time, since in the end it's those things that actually hold a team together.
not be people with crap social skills are better than people with good social skill
but rather, people with crap social skills are easier for your competors to miss
good tech skill + good social skill = good and expensive
good tech skill + poor social skill = (I'll let everyone make up their own mind about how good they'll fit) definately less expensive though
any trait you overfit for is something you giving up other traits for somewhere else
Since I've introduced arbitrary numerical scoring, I guess by "negatively weighting" I actually mean doing something equivalent to mutiplying their overall performance by 1 + scalefactor*(technical answers score - generic interview answers score) , but I'm assuming in practice most interviewers use their intuition rather than subjectively scoring every answer.
I'm assuming your amazingly productive friend aces the technical questions at least as impressively as the "convince me you'll have grown with the company after 5 years, even if you actually only see this as the bottom rung of the ladder" ones.
A reasonable theory; I'm skeptical as to whether it would turn into better performance in hired candidates.