Mango's enhanced native support for Internet Explorer 9 supports hardware-accelerated graphics processing. Combine that with HTML5 and you have the potential for extremely responsive, fast-running, interactive games and videos on a mobile Mango smartphone.
Microsoft's Windows Phone 7 Mango update faces serious competition from Apple's iPhone 5 and Google Android Icecream Sandwich when they are released. Its feature set must include factors that are either not present in other smartphone and tablet OS's, or make the features in those OS's pale by comparison. Enhanced native support for IE9 could be that feature.