An accelerometer is one of the mandatory sensors that all Ultrabook™ devices must possess. This sensor can detect motion and gravity. Use cases for this sensor are innumerable.
Ultrabook™ devices support more than one screen orientation such as landscape, portrait, face-up, etc.
Current laptops might not be best suited for use under certain circumstances such as in cars or outdoors in direct sunlight as laptop screens usually have some readability and legibility constraint
In a previous post I explained how adding sensors to HTML5 app is possible in Desktop mode but not yet supported. You can get it to work with a Google extension. Read this post.