Author's Note:
After reading my reviews, I guess I should clear some things up. As it says in the first chapter, before the purification, his power was already 5 million. Therefore although I didn't put this in, every one of Goku and Vegeta's descendants kept on training. Also, purification can kill someone, since their DNA is being altered, they can die in the process. And I think his training explains how he can use all those moves. The legend of Goku also wouldn't be forgotten, or Vegeta for that matter.
Thanks to all reviewers, Lanky Nathan, Jimbo, BillyTalentPhuckingROCKS, Happy-Hippy.