Speaking with Videogamer.com, director Katsuhiro Harada explained his reasoning:
Why we locked the characters originally was that in the arcades, it was kind of to extend the life of the game by gradually unlocking characters. And also with the home versions as well, because you can rent games or whatever, it was to protect us against that.
Thats kind of outdated now though, especially with online play. If we were to have locked characters it would irritate a lot of people, to be playing against others online and to not have all the characters available. So I think its no longer useful.</blockquote>
Tekken 6 will feature 40 characters all available from the start.