Readability is exactly why sites need to enforce a maximum chars/line. Don't ask your users to constantly resize their window just to read your content.
I got a big screen specifically so that I can have multiple windows on my screen. Having a site decide to be in charge of sizing instead of allowing me to choose is user-hostile.
You're always in charge of your browser width and zoom. With the use of relative ems, a designer can accomplish a sane line length for any combination of settings.
