Explains how Yahoo! Finance generates the Market Cap quotes.

Yahoo! Finance calculates the market cap using the shares outstanding data from Capital IQ's quarterly or annual report.
   
Currently, we receive this data from Capital IQ once a quarter. If a new report was filed after we received last quarter's updates from them, the shares outstanding will not reflect this updated data on Yahoo! Finance.

We are working with them, so we can receive daily instead of quarterly updates. We hope to have this change implemented, as soon as possible, but it may be a few months away since it involves changes for both Yahoo! and Capital IQ.