The user experience when viewing webpages is improved by actually showing a lower-resolution image while the crisp high-resolution image is being downloaded (however slowly), similar to progressive JPEGs.
Depending on the data contract, the user experience when viewing their mobile phone bills might be affected negatively though.
The iPhone 4 and 4S also "lie". It's not really a lie, though. The displays are intended to have higher pixel density, not more screen real estate. By reporting the "incorrect" size, websites are actually sized consistently across all generations of iPhones and iPads, but the retina devices render the same content with higher resolution.
PS: you may wish to add a "(-webkit-min-device-pixel-ratio: 2)" clause to your media queries if you want to target retina devices.
Depending on the data contract, the user experience when viewing their mobile phone bills might be affected negatively though.