I suspect that Apple doesn't necessarily care to have the largest browser market share on Windows.

If they did, Safari on Windows would look and feel more like a Windows application. As it stands, it's a very opinionated application, with foreign-looking scrollbars, text antialiasing that works differently from ClearType (they may have changed this by now, I haven't looked), etc. Comparing market shares between these browsers with the assumption that they have the same goals might be a bit off.

[edit]: I've also noticed a lot of people I know living over in the Windows world seem to harbor an uncontrolled hate-on for iTunes and Quicktime. Since these are often associated with the installation of Safari, that probably doesn't help Apple's position. Does Chrome come with any "unwanted" extras?