Why do people get so anal about it, whether you believe in a god, the God, many gods, no gods, whatever, it dosent matter. When you are in court, no one knows whether you are telling the truth or not. By acknowledging a higher power, you understand that you can be punished if you lie. And no I dont mean a biblical plague or anything like that. Hell, a damn tricycle is higher up than a lot of people I see in this world, so if they lie, that damn tricycle can strike them down. Or you don't believe in three-wheels either?
If you really wanted to, you may be able to get them to change it to "I swear to tell the whole truth and nothing but truth so help me a power greater then me in all premises that I know to my greatest knowledge, that could take me down for any time that I abuse the trust that is being given to me." But guess what, thats a pain in the ass, and "god" pretty much sums it up. And look I don't capitalize god, because I don't really believe in the God, but I do believe there is a power greater than us, because humans are weak freaking creatures (hence all this bickering over wording) so I obviously still believe in a god, whatever it may be.