The revival of Chicago has moved past A Chorus Line as the 4th longest running show ever. It surpasses A Chorus Line. The original production open in matter of days of ACL and was over shadowed in its time. I saw the original production with everyone but Chita Rivera as she had left the show. It was one of the first Broadway shows I ever saw.
IMHO I think Chicago is better show and it lights of what has happened with public trials on tv and other medium the show has become more relevant than it was when it first opened.
The show keeps on being rediscovered my younger audiences. I read that they get a lot of High School groups seeing it and for man teenagers this is the first exposure to Broadway.
It also helps with the revolving door of actors every 4 months or so. Some well known some not.
I've wondered if this revival would be doing as well as it has been IF...
-it had used the original book and score - Not the streamlined Encores! concert version.
-the movie version of it had tanked.
And as DR elmore pointed out, the producers have been able to keep this show running via some very blatant "Star Casting". Some of the leads come in for a few months, some only come in for a few weeks. However, it is nice seeing that they're starting to feature some relative unknowns lately such as Nikka Graff Lanzarone.
As for it being the first Broadway show for "man [sic] teenagers", the Weisslers have a very good educational program tied into to the show. They will hold a seminar-like presentation during the day, then the students will see either the matinee or evening show. Of course, bringing in Guest Stars such as Usher, Christie Brinkley, Kara DioGuardi (who starts next week), etc., also brings in some audience members who might otherwise not consider seeing a Broadway show.