Notice that this is the age where everybody’s capable of viewing anything online anywhere. That means that despite the idea that web development mainly caters to computers, ‘computers’ aren’t necessarily stuck in your home with the typical screen resolution that a fixed 960 grid would do well on.
Responsive design is a great practice that each designer should learn. I myself am not that well attuned to that although I’ve been self studying a lot to actually learn and master this feature.
Basically, it’s a matter of using and calling relative styles and settings, the usage of em’s rather than px’s, dependent on your visitor’s device.
And notice how Smashing Magazine’s current layout is just a great example of how responsive design is pro.