While I am sure some websites leave that space for ads. There is decades worth of research regarding readability. The amount of characters on a line influences readability a ton.
Certainly, on 16:9 ratio displays, text taking up the entire page width is just not ideal for most people. Most research points at roughly 70 characters per line being the ideal. Which means that even on a contemporary 4:3 display with a 1024x768 resolution, there will be some space on either side.
Certainly, on 16:9 ratio displays, text taking up the entire page width is just not ideal for most people. Most research points at roughly 70 characters per line being the ideal. Which means that even on a contemporary 4:3 display with a 1024x768 resolution, there will be some space on either side.