Yup it comes to no surprise. Windows is the majority platform and most common users tend to use the apps which come with their machines. IE comes with everything by default so many people use it. On Mac platforms the same could be said about why so many of them use Safari.
I use IE for sites which doesn't support the browser I use (Chrome). For example OWA (outlook web access) are sometimes configured so that when you login using IE, it gives you the full-version OWA experience but when you login using Chrome, the server provides only the lite-version experience.