I disagree. You always leave the edges empty or at least put non-essential information there. There are so many contexts where the edges aren't there, such as:

- print (not really applicable to the web) - projectors/TVs (my TV cuts off ~5% from each edge) - sticky notes on the edge of the monitor - anti-glare screen covers

It also feels cramped to read at the edge of the screen. I like having the negative space there to frame the text.