Could anybody explain why there is such a difference between text and image? Is this just because the file sizes are different or has that a different cause? I

Could anybody explain why there is such a difference between text and image? Is this just because the file sizes are different or has that a different cause? I really like to "out-of-the-box" comparison, but as others already have stated for apache that doesn't really make sense because apache just doesn't perform well without any configuration changes.