That the wheeled bag was created by a Northwest pilot, 22 years ago?
http://www.theage.com.au/travel/travel-new...90923-g133.html

Aside from that interesting fact, the article also links to an interesting site I didn't know about: Luggage Limits. Apparently it lists applicable luggage limits for each airline, and breaks if down based on flight number (example regional aircraft sometimes have lower limits etc.).
http://www.luggagelimits.com/