Quote from the page above " Light and Medium Utilization Reserved Instances also are billed by the instance-hour for the time that instances are in a running state; if you do not run the instance in an hour, there is zero usage charge. Partial instance-hours consumed are billed as full hours. Heavy Utilization Reserved Instances are billed for every hour during the entire Reserved Instance term (which means you’re charged the hourly fee regardless of whether any usage has occurred during an hour). "
I think you pasted the wrong link, though. Here's the page which contains that quote: http://aws.amazon.com/ec2/pricing/#reserved
havent done a check to see if he was taking into account the discounted hourly price or just adding on on-demand hours...