Here's an interesting by Richard Just in The American Prospect dedicated to that defense. He makes some good points:

Without the U.S. News rankings, elite colleges would likely be turning over even larger numbers of coveted spots in their undergraduate classes to athletes, imperiling racial and intellectual diversity at the nation's top breeding grounds for future scholars and leaders. And state schools -- accountable to lawmakers and, ultimately, the public -- could find themselves pressured to squander even more money in pursuit of national championships many of them will never even come close to competing for.
... Sports is the only thing colleges do that can be quantified. It provides the only concrete claim a college can make to being better than another college. Is Harvard better than Yale? Impossible to say. But which school won the Harvard-Yale football game last year? That's an easy question to answer.
The U.S. News rankings have changed that. Critics of the rankings charge that they're meaningless, but the critics are missing the point. Of course it's meaningless to say that the University of Virginia is the twenty-third best school in America and Georgetown is the twenty-fourth. But the point is not whether the rankings are accurate in any sense, as if such rankings could ever be anything but vaguely arbitrary. The point is that by trying to quantify educational quality -- however imperfectly -- U.S. News sends a strong message that college academics matter and provides an incentive for universities to counterbalance the longstanding athletic arms race with an academic arms race. And that balance is a good thing for higher education as a whole.
.... In the absence of U.S. News, the only quantifiable game in higher education is sports. And that situation has real consequences for educational quality.
...By creating another highly-publicized arms race, U.S. News has diluted the sometimes-harmful influence of the athletic arms race -- and somewhat refocused the public's attention on the primacy of academics in higher education. In April, everyone knows who won the Final Four. In January, everyone knows who won the Bowl Championship Series. And now, in September, a decent percentage of Americans know what the number one school in the country is -- and more importantly, how the public schools in their states, which are funded with their tax money, measure up. Whether these ratings are impeccably fair is less important than the fact that they exist. It's the spotlight they shine on academic quality, not the precision of the measurements, that really matters. And it seems safe to assume that without them, the pressure for colleges to make unwise choices in pursuit of athletic glory would grow even more overwhelming than it already is.