Bob,
Optimal line width is nice, but because this site does not dictate font size or browser window width, or screen resolution, there is no way we can tell how the site will render in any situation. So we cannot design a solution that will work nicely.
I agress that too long lines are harder to read, I just do not know of a solution that would not create another problem.
Possibly a <div> with a width of so many ems would work, but support for dimensions specified in ems is not very reliable in current browsers.
