2011 Macbook Pro battery drainage

My new 2011 MacBook Pro 15 provides a battery life of just 3 hours which is way below the promised 7 hours. I talked to the technical support team [Case #: 209175232] to receive a response that it is reasonable as I am streaming online video. This is my first Mac and I am highly disappointed to see the difference in promised vs actual battery life. Have some one experienced such issues? I am wondering if I should return this for replacement.