Actually my Honda CB 900 F Hornet (919) is way more comfortable on longer distances than my Yamaha XVS 650 Dragstar was. Last summer on our trip to France we rode about a 1000 km (620 miles) on the first day, it took us about twelve ours, and surprisingly neither of us had sore buts.
In 2002 we were on a single day trip on the Dragstar, and ended up doing around 700 km (430 miles) and at the end of the day we could hardly stand.
I heard an explanation once that it’s because on a sport bike your body weight is evenly distributed on your hands, legs, seat and most important inner thighs. On cruisers, because of the upright riding position, the wide handlebars and the forward controls, your weight is placed directly on your coccyx giving you sore buns faster.
Goes to show, cruisers are not necessarily the mile eaters people think they are and naked bikes are not just for blasting around town. But who cares if you get a sore but or aching shoulders, when you’re riding your bike of choice into the sunset. There’s no beating, feeling used after a long day on the bike and several hundred miles of road behind you is there?