You're undervaluing time spent locked up.
EDIT: On further thought, I'd go for much less, I think. It's really just a comparison the money offered against A) the amount I'd expect to earn in those 3 years, B) expected loss of lifetime income due to the time lost and/or resulting stigmas, and C) personal discomfort/inconvenience of the lockup time.
Hard to figure the latter two, but I expect even half a million would tip the balance in my case.
I also think your question can be generalized.
Waiting for the train, you hear the announcement "an uptown A train is 4 minutes away from west 4th st." "What if these are the last 4 minutes of my life?"
Waiting at a red light, looking at the countdown clock in the other direction: "What if these are the last three seconds of my life"?
I've buried enough people in their middle age by now to not take the next three years for granted.
You can't take it with you.
Look at it as getting paid $6,000 an hour to read books for three years. Not the worst gamble someone my age could take.
Think of it like a three-year, $100 million sabbatical "upstate." That is enough time to read through the great books. Room and board are covered and there is a commissary for personal items.
Remember: the premise here is that once you do your bit, you're set for life.
Personally, I'd stick to the PowerBall for a get rich quick dream.