In the screenshot http://www2.pic-upload.de/11.12.09/cuji68t225hx.png pay attention to the elements marked with number 1.
use.perl.org makes use of most of the width of the viewport thanks to its flexible layout. This is not the case with b.p.o where margins and content width are fixed. The result is not as bad as over at perldoc.perl.org, but nevertheless it's not a pleasure to read longer texts that way.
Readability suffers as lines grow long. Common wisdom is not to allow lines in text to get longer than about dozen average words, at most.
There is an argument to be made in favour of giving the user the ability to make that choice themselves, by resizing the window to a comfortable size. However, most users do not behave that way for a variety of reasons. A limited-width layout is the correct default. It might be worth offering an optional non-default full-width style, I dunno.