University rankings would be more informative if they took into account graduates' contributions to a country's international economic competitiveness. Although institutes in the United States and the United Kingdom currently top the university rankings, the most successful technology-based export industries are dominated by northern and central Europe, as well as by Asian city states — the per-capita exports of which are also several times higher.
Rankings are heavily influenced by citations, but these represent little more than symbols. They are comparable to the less-than-worthless collateralized debt obligations that drove the recent financial bubble, and, unlike concrete goods and real exports, they are easy to print and inflate.
Financial deregulation led to short-term incentives for bankers and rating agencies to overvalue their collateralized debt obligations, bringing down entire economies. Likewise, today's academic rankings provide an incentive for professors to maximize citation counts instead of scientific progress (by coincidence, both types of incentive were invented in the United States). We may already be in the middle of a citation bubble — witness how relatively unknown scientists can now collect more citations than the most influential founders of their fields.
It may be easier to collect citation indices than employment histories and other statistics about the impact of graduates on industry, but modifying rankings to take these into account would be worth the effort, particularly for institutes and countries that are currently traded below value.
Note that I write from the country with the most citations per capita and per scientist.