November Internet applications traffic

According to Nielsen//NetRatings (PDF) Windows Media Player is the top non-browser based Internet application for the month of November. 48 million unique users. AOL Instant Messenger and MSN Messenger are surprisingly close at 28.3 million and 27 million respectively. Why is Yahoo! the top instant messaging program in the workplace? It installs without administrative privileges and easily bypasses the corporate firewall. Why does MSN Messenger have 37% market share? According to WebSideStory Windows XP is used by about 35% of Web users worldwide. 42% of Google users in October and November 2003 used Windows XP. Windows XP just happens to install Windows Messenger by default, asks you to sign into your computer with your Passport, and launches on startup. Yes I am comparing U.S. market numbers to world market numbers, but MSN Messenger seems to be used primarily at home by about the same population as Windows XP users.