Gravity is a theory. Which means it has significant scientific evidence behind it, consistently reproduceable results, and scientists have an extremely high confidence that the results will continue to be true in the future.
What you have here is a hypothesis. Any crackpot can make up a hypothesis. I hypothesize that mutant alien space creatures came down in a space ship crash, ate the insides of humans, and inhabit their flesh, walking around. They are only identifiable by their intense desire for sugar water and oddly deep voice.
That doesn't make it true. The burden of proof then lies upon me to prove it. Others have to be able to reproduce my findings, and significant scientific evidence would have to pile up, like if people managed to escape the memory wipe flashy thing from the men in black suits, and had video evidence of the creatures' swath of destruction... but that hasn't happened, so it's still just a hypothesis. If, and only if, pretty much every scientist is sure it's true, does it get to be a theory.
Cold Fusion is a hypothesis, one which has not proven to be highly reproduceable. And a hypothesis it will stay until it is fully understood and proven.
As for the E-Cat... my scam-dar is going off hardcore. Anyone would be a sucker to invest in that thing until he actually proves it works.