[Gys]

Peacekeeper itself says they focus on js.

http://peacekeeper.futuremark.com/faq.action:

Peacekeeper measures your browser's performance by testing its JavaScript functionality. JavaScript is a widely used programming language used in the creation of modern websites to provide features such as animation, navigation, forms and other common requirements. By measuring a browser’s ability to handle commonly used JavaScript functions Peacekeeper can evaluate its performance.