OK, this is now an option in your
account preferences once again...but I remain dumbfounded, as it feels like I've built a house, and you're all upset because you'd prefer the knobs in the middle of the doors instead of the side!
Too often these days designers are putting "readability" and implementing the latest in-vogue-standard ahead of well written, well laid out and engaging content.
"Readability" and "well-laid-out and engaging content" are the same thing, and constrained line length isn't exactly the "latest in-vogue-standard". Check out any book, magazine, or newspaper printed within the last few hundred years and take note of its line lengths.
Could be because some people like more content to be displayed.
That's mostly an illusion, though. Here's another look at the screenshots you posted:
Which one has more "wasted space"? Which one "displays more content"?
The pink bars cover the exact same area in terms of pixels, but the one on the bottom requires you to move your eyes - and your mouse - across the entire width of the screen (at least 14 inches or so) to navigate all the links and to line up the thread titles with their forums.
With the layout on the top, all the same information is right in the middle of the screen, no more than a few inches away - and the only "cost" is one less forum link. The space on the side may be "blank", but it is not "wasted".
In text-heavy thread pages, you can do another experiment by measuring the height of the page before and after changing its width. On the first page of this thread, for example, with a monitor 1600 pixels wide and the new site template's default width of 980 pixels, the height of the page is 9155 pixels. With the "wide screen" template enabled, the height is 9025. That's about the height of a single avatar - barely another notch in your mouse's scroll wheel.
The ultimate point here is that widescreen monitors are awesome for videos, games, and productivity, by allowing you to place several different windows side-by-side. They absolutely suck for reading content on the web with your browser in full-screen mode. (A lot of
power users and programmers put their wide-screen monitors in vertical orientations. Give it a try sometime.)