I think a better definition of a console's lifespan should be the date where it stops being manufactored by the console developer. Xbox might get a game or 2 per year but its not possible to purchase it at a retail level anymore unless through second had.
With regards to the list, the dreamcast would be dead since 2001 where Sega abandoned the console to its fate, but there were still minor game being produced on the system once in a while (mostly Japan only) and it had a fairly active homebrew scene.
The Sega Genesis (Megadrive) on the otherhand is STILL being manufactored in an official capacity in Brazil by Tec Toy albeit in a handheld iteration (released in 2007).
Sega officially began to discontinue the the Genesis in 1995 but sold the license to other parties for specific regions.
