Well at the same time if he fought a gantlet of opponents, say like Froch, maybe he'd have a loss or two. If he fought Cotto, Margarito, Williams, Mosley, Cintron, all those guys when the division was HOT, rather than retiring for two years, maybe he loses one of those fights. But like Floyd said he's about self preservation. I have to speak on this Magarito got beat by Willaims 8 months after calling out Mayweather (which was really Bob Arum and Top Ranks way of trying to resigning Mayweather), then Williams loses to Quintana.
Mayweather fought Mosley, Cotto, and Manny ducked him two times. Paul Williams lost out on the fight because the Quintana fight, and Margarito is and always was a overhyped BUM.
Devon Alexander fought Lucas, Maidana, Bradley, and Khan probably next for all the hate and disrespect he gets Devon is a real warrior not fighting rematches like Froch.
That's why I never trip on an undefeated record. We look at past greats Leonard, Robinson, Ali, Archie Moore, etc, these guys fought very very tough opponents back to back to back, so naturally a guy is going to lose here or there because the competition is so fierce and frequent. lol.. People need to stop overhype the past fighters all the guys you listed up top 75% of their resume is full of bums and rematches. The may have fought more in the past but most of those fights were against bums. Mayweather has fought nothing but top rated 147lbers and in most cases a top 10 P4P fighter.
Not taking away from Floyd, he's AMAZING in the ring, but there is some truth to fighting once or twice a year that probably has assisted in his undefeated record. There is of course politics and money that factor in. I'm sure Robinson wouldn't fight twice a month if he was making $40 million a fight either!