I'll let @danielsaori handle the where he gets the data from, he is the expert on that...
On the math, you have to realize that the profitability changes with the price of steem... at $3 value of steem if you do the math, the breakeven after curation is roughly 1.9x... this changes all the time. You have to do the calculation at various steem prices and you will see what I mean.
On the other point, if someone pays for a vote and for some reason it still gets dusted (its happened 8 times in roughly 4000 votes) then the full value gets refunded to the user. So this is not an issue at all.
So glad you're on it @davemccoy. I don't have a hope in hell of working all that out! 😍