In a new post on the World Blog, Microsoft explains how it optimized Word for the ARM-based Windows RT. You can read over here how they optimized the text processor to enhance battery life and limit memory use.
The Word team firmly believes that typing and scrolling are core scenarios for Word. Almost any usage of Word will involve typing and scrolling to some extent. Because Windows RT devices are more resource constrained than typical desktops, we made it a goal to ensure that typing and scrolling in Word on these devices continues to look and feel great. It took some effort to make that happen, but in the end we’ve delivered well on our goal. Scrolling via touch in Word 2013 on a Windows RT slate looks and feels fluid and natural. Typing feels clean and responsive, and a smooth yet subtle cursor animation enhances every keystroke. The overall experience feels solid.