The problem with math is that some people suck at it.
Problem 1 is that oil is not gasoline, and a barrel of oil makes 19-20 gallons of gas out of 42 gallons of oil, so based on the raw numbers in the email, 224 million gallons of gas is closer to 11.5 million barrels of oil, which, at $70 a barrel, would run just over $800 million.
Problem 2 is that's only 1 year of savings. If we can assume that each clunker would have stayed on the road another 5 years, that's $4 billion in savings.
(note: C4C is still retarded, I didn't support it, the math is indeed crummy which is why it was never about "green" cars really, and most of the clunkers weren't being driven at all, yet alone 12k miles a year. Still, bad math is bad and needs to be pointed out).