Limiting characters per line within a column of text is reported by many readers to ease reading.
While limiting the entire content's width also happens to limit the number of characters that can fit in a line, limiting the width of the content of the page is doing a lot more than just that.
To prove by example that other approaches can achieve the same goal, one could cite newspapers, that produce several columns of text with short lines. In passing, in newspapers the columns are very narrow because it is hard to hold it flat in front of you to read it, something anyone reading news on actual paper has noticed.
It is also quite possible that, by digging into the reason why 80~100 characters per line are reported to maximize readability, one would discover other ways to achieve higher readability, the actual goal. Again, I do not expect anyone to believe me without proof by example: long text lines with alternating background color (as in tables) is a far-fetched idea, but it could also feature high legibility, and that sort of idea can only come out of seeing the question from this broader perspective targeting the final objective.
Note/disclaimer: I am myself indifferent to line length, except when it goes below 50 characters.