There’s a little thing in the browser called a User Agent String. It tells the website and its advertisers what type of browser and operating system you are using. They use it to target ads, and some of the smarter websites use it to feed different pages to different browsers. This is how you get a mobile site on your iPhone or Android phone, among other things.
Microsoft is obviously ignoring the User Agent. Trying to feed me IE 9 on a Mac running Chrome is wasted ad money. Even if I could download Internet Explorer 9, I wouldn’t. But I can’t. They don’t make it for Mac.
Idiots in charge