Also, fighting less often gives less chance for upsets. I suppose this is also why the world heavyweight champions do quite well on the list.
If it doesn't bother you that Wlad won't fight his brother, so he lets him hold a piece of the crown, you could include Wladimir Klitschko on your list right next to Lewis at 6 years. Also, Johnny Kilbane held the featherweight title back when there was only one of them from 1912-1923. There's a problem with your methodology, with your not needing the best fighters to defend a title against the best in their division, and them just having to be the best at their weight class. It's not actually based on anything but an eye test and a general opinion. If that were enough we wouldn't need the fighters to actually get into the ring and compete. It doesn't account for upsets like the recent Pacquiao/Marquez fight, or Tyson/Douglas, heck Ali was 8-1 going into his fight with Liston, he was a massive underdog to beat Foreman, etc. Anything can happen. People decline or get exposed. If you just look at Juan Manuel Lopez' record going into the fight with Salido it's no contest at all. If the best no longer have to fight the best to get the crown then you can award the title without a victory then take it away without a loss. Maybe you feel that Harry Wills was the best heavyweight of his time instead of Dempsey so you make him the champ over Dempsey without them ever having fought. Or if Ali is still champ but not the best fighter you cut his reign short and give it to Foreman or Holmes who were in their primes. Why wait until they gain a belt before you declare them dominant? Lots of guys didn't even get a chance to fight for a belt. Then another problem I see with breaking the reigns into years is that some guys fight once a year and some guys fight ten times a year. It's more fair to site the number of title defenses when determining the length of a reign.
For your consideration, from http://fivedogs.tripod.com/misc.html Most consecutive successful defenses Division Name Title Years Defenses Heavyweight: Joe Louis World (1937-49) 25 Cruiserweight: Anaclet Wamba WBC Title (1991-94) 7 Light Heavyweight: Bob Foster World (1968-74) 14 Super Middleweight: Nigel Benn WBC Title (1992-95) 9 Middleweight: Carlos Monzon World (1970-77) 14 Junior Middleweight: Gianfranco Rosi IBF (1989-94) 11 Welterweight: Henry Armstrong World (1938-40) 19 Junior Welterweight: Julio Cesar Chavez WBC/IBF (1989-94) 12 Lightweight: Roberto Duran World (1972-79) 12 Junior Lightweight: Brian Mitchell IBF/WBA (1986-91) 12 Featherweight: Eusebio Pedroza WBA (1978-85) 19 Jr. Featherweight: Wilfredo Gomez WBC (1977-83) 17 Bantamweight: Orlando Canizales IBF (1988-94) 16 Junior Bantamweight: Khaosai Galaxy WBA (1984-91) 19 Flyweight: Miguel Canto WBC (1975-79) 14 Junior Flyweight: Myung Woo Yuh WBA (1985-91) 17 Strawweight: Ricardo Lopez WBC (1990-99) 21 Longest uninterrupted title reigns Division Fighter Reign Heavyweight: Joe Louis 11 years, 7 months Cruiserweight: Anaclet Wamba 4 years, 10 months Light Heavyweight: Archie Moore 9 years, 2 months Super Middleweight: Chong Pal Park 3 years, 6 months Middleweight: Carlos Monzon 6 years, 9 months Junior Middleweight: Gianfranco Rosi 5 years, 2 months Welterweight: Felix Trinidad 8 years, 5 months Junior Welterweight: Julio Cesar Chavez 4 years, 8 months Lightweight: Benny Leonard 7 years, 8 months Junior Lightweight: Flash Elorde 7 years, 3 months Featherweight: Johnny Kilbane 11 years, 4 months Jr. Featherweight: Wilfredo Gomez 5 years, 10 months Bantamweight: Orlando Canizales 6 years, 5 months Junior Bantamweight: Khaosai Galaxy 7 years, 1 months Flyweight: Jimmy Wilde 7 years, 4 months Junior Flyweight: Myung Woo Yuh 6 years. 2 months Strawweight: Ricardo Lopez 9 years, 8 months