I believe the new series gradually reveals Atom's past in memories for two reasons:
1. to make it sufficiently different from the motion picture that will be relesed soon. Because this new series was created because the film was behind schedule, and Sony wanted to make 4/7/2003 a special day. But because a plot that was too similar to the motion picture's might take away from the film's popularity, the flash backs are therefore used to reveal Atom's earliest days.

I am assuming that the film will use a different plot.

However, I have seen eps 1 - 34, and lately, there have been no flashbacks. The scene in ep 1 (I think) where Atom has just realized that he can fly, and he looks into a reflection in a glass window, but sees Tobio rather than himself, exemplifies these flashbacks.
2. I likewise think that the creators felt the need to distinguish this series from the previous two. Doing so from the very first episode maximizes chances that people will watch it.
However, as I do not live in Japan, I am making assumptions that even with the exitement about Atom's birthday, and so many products not just toys, bearing his image, the producers nevertheless wanted to be sure that nobody would dismiss this third animated series as just a remake of the previous series.
