Correct me if I'm wrong, but doesn't Dropbox use AWS? (Or at least did until recently.) The two services' pricing (on a per GB basis) is within the same ballpark.
Dropbox has received a quarter of a billion dollars in funding.
According to Drew Houston at Websummit last week, they haven't spent any of that money.
So all of their acquisitions and burn has come from (crunchbase caveat) ~7MM? There's some missing pieces to be sure, but suffice it to say that having that much cash in your back pocket allows a different set of considerations.
Drew said the same thing at TC Disrupt in SF this year. Reading between the lines: All the acquisitions and ability to pay 300+ staff without needing to touch a massive $250 million pot of money is basically telling the market (eg: Box): "We can play the enterprise game very well and have the revenue to prove it"
I'm sure Dropbox gets better volume pricing than Everpix did.