As you likely know, the GMAT is a computer-adaptive test (CAT), in which your score is calculated by an algorithm that provides you with harder questions (and higher score returns) when you answer previous questions correctly, and with easier questions (and lower returns) when you've answered previous questions incorrectly. So, the difficulty levels of the questions that you answer correctly or incorrectly has more bearing on your score than does the sheer number of correct or incorrect answers. It is not at all unusual for someone to miss a greater number of questions and end up with a higher score, provided that the missed questions are all on the upper threshold of difficulty.
Please visit our blog at http://blog.veritasprep.com/2010/08/und ... rithm.html
to learn more about the GMAT scoring algorithm and Veritas Prep test taking strategies.