You do know that these last two quotes are taken out of context, do you not?

John Adams is also purported to say: "The general principles upon which the Fathers achieved independence were the general principles of Christianity…I will avow that I believed and now believe that those general principles of Christianity are as eternal and immutable as the existence and the attributes of God.”
[June 28, 1813; Letter to Thomas Jefferson]

The truth of the John Adams quote is that he was expressing a frustration with the bickering done among religious people; the full quote goes like this:

"...The Parson and the Pedagogue lived much together, but were eternally disputing about government and religion. One day, when the Schoolmaster had been more that commonly fanatical and declared if he were a Monarch, He would have but one Religion in his Dominion. The Parson cooly replied 'Cleverly! You would be the best man in the world, if you had no religion.'
Twenty times, in the course of my late reading, have I been upon the point of breaking out, 'This would be the best of all possible worlds, if there were no religion in it!!!' But in this exclamatic I should have been as fanatical as Bryant or Cleverly. Without religion this world would be something not fit to be mentioned in polite company, I mean Hell..."

Please notice how he ended the quote.

Regarding Thomas Jefferson's quote, you must realize here that "perverted" does not here insult the ideals of Christianity but rather upholds them as right, whereas the Christianity he found in practicality seemed to have little to do with the ideals of Christianity. One must not judge a religion by the people who claim to adhere to it; it must be tested based on its principles.

By the way, the quote is paraphrased, leaving out some important words that show his opinion of Christianity to be to the contrary:
"...those who live by mystery & charlatanerie, fearing you would render them useless by simplifying the Christian philosophy, the most sublime & benevolent, but most perverted system that ever shone on man, endeavored to crush your well earnt, & well deserved fame." - Thomas Jefferson to Joseph Priestley, Washington, 21 March 180 (bold mine)

Though the founding fathers may not have been as devout as some would like to make them out to be, upon careful examination it will be discovered that it was upon Christian principles and faith in God as Creator that this nation was founded. Again, I point you to the Declaration of Independence; without an external God guaranteeing our freedom regardless of our opinions, we have no anchor of freedom on which to rely. And as proof of that, I'd like to point out that you're lucky to be born; many of us have not received even that freedom.

"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness." Thomas Jefferson, Declaration of Independence