The Google Toolbar now can override keyword search in the IE address bar, using Google instead of MSN Search.
Defaults have always been a big advantage to MSN Search. Windows and IE have dominant market share. Many novice PC users apparently don't even know what search they use; they just type keywords in address bar and search, so they use MSN Search by default.
But now, the Google toolbar makes it easy to change the IE defaults to use Google instead.