Way more reasons... Duathlons have a degree of tactics/pacing from the 2nd run that are not part of triathlons. Cook the swim? Are your arms tired, baby? No problem - you don't need them for the rest of the race. Cook the first run? Are your legs worked? Yeah, totally screwed. Think that's no big deal? Give it a whirl... I was super happy with my du run last weekend. 1st run was a bit slower than my best, but 2nd run was strong - best ever. If I had been on the bike since my last race, I would have really cleaned up...