WMG: A.I.: Artificial Intelligence

The David robots set off a series of events that lead to the post apocalyptic super-mecha seen at the end.
A perpetual child would get really old, really fast, not to mention kinda creepy after awhile. Eventually, the company released upgrades for the Davids that included enhanced intelligence, and the body would be brought in and changed to simulate growing up. Eventually, the Davids reached adulthood. This would bring forth a brand of robot never before seen; robots that had no purpose other than to live. Immortal beings with supercomputers for brains. They upgraded themselves/made robots for themselves until eventually, the super-mecha were made.

The super-mecha destroyed humanity.
With the way that humans treated robots, and the way robots were getting more and more advanced, an uprising was only a matter of time.

The film takes place in the same universe as Spielberg's version of Minority Report.
A.I. takes place about thirty or forty years after the events of Minority Report.

Precrime existed, but it's underwater with the rest of Washington D.C.

The fish that circle David instead of scattering are early versions of mecha evolution.

The ending with Monica and Teddy didn't really happen.
Rather than actually cloning Monica, the super-mecha programmed the fantasy of the perfect day into David. This would explain the weirdly convenient one-day clause for cloning, as well as Teddy's implausible survival.
  • It was stated that it was a kind of "memory track", or something like that. It was really in David's head, thanks to the super-mecha.

The David robot's program is that it can See Dead People
It was a robot created by Dr. Egon Spangler of the Ghostbusters. It's "memories" suggest that this particular one shown in the movie malfunctioned.

Gigolo Joe lives.
They found out he wasn't the murderer and he went looking for David only to find himself trapped and frozen.
  • He eventually evolved into the leader of the future mechas.

The Technicians were planning on making David a real boy.
Since he was able to think, feel and dream like a real human their next logical step was to make him as human as physically possible. Like make him be able to eat other bodily functions. Because he was wrapped up in his own anger and delusion he didn't see it through when he looked for the Blue Fairy.

Cybertronics did not tell Doctor Know where to send David
Artificial Intelligence everywhere was becoming sentient, right under humanities nose. Doctor Know was a part of that, recognizing that he was speaking to mecha and sharing one of the awakening mecha society's own legends that Man-hattan was a place where mecha could live eternally because none had returned. (Yes, Professor Hobby says they interfered then, but I like this better as better foreshadowing of the ending, and in my IMHO They Wasted a Perfectly Good Plot).

Professor Hobby was running for it.
He sure is gone for a long time after he leaves David, isn't he? He said he was going to get his team, but he seems to live alone. Hobby is a recluse and David was a recognized rouge robot who had just destroyed another. He talked David down and split when he had the chance, notifying the police.