I've owned two sport touring bikes, at least they were according to their makers; a 2004 Ducati ST3 and my current 2005 BMW R1200ST. I did a comparison thread on here. Both bikes were around 500 pounds wet, which is 200+ pounds lighter then the Honda ST's. I've always thought of sport tourers as more upright sporty bikes with hard luggage. To each their own.
As far as the "can't define it but know it when you see it", that was a quote from the Supreme Court regarding pornography.
2013 Yamaha XT250 * 2012 Kawasaki Ninja 250 * 2007 BMW G650X XChallenge * 2005 BMW R1200ST * 2003 Yamaha PW80