Their article pane resizes to an extent, but I assume it stops expanding after a certain size because they don't want to exceed an optimal width for readability [1].
Without being able to see it on your monitor, can't tell for sure.
Right, but couldn't they expand the pane but leave the text at the same ratio? The way it is now, the right-hand scrollbar leaves the right side of the window[1], which is kind of weird. Adding whitespace on the sides might be a better way to achieve the same goal.
[1]: http://i.imgur.com/doaiMyc.jpg