I think that falling into the trap of treating social skills and technical ability as a trade-off is a mistake. It's a hackneyed stereotype that I don't think has ever been true--but I'd imagine it has sometimes led to people expressly trying to seem socially abnormal in order to fit the idea of someone technically adept. I recall an anecdote about how a younger mathematician at a top research institution took up running his hand along the wall as he went places in order to seem odder, since it seemed like the best senior mathematicians there all had odd quirks. I'd imagine that the idea that social skills and technical ability are inversely correlated has led to similar things.
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.