I simply don't believe this story. If you have $100+ million to throw at as fundamentally simple a product as Dropbox is, you have more than enough to make a good clone of it. It's not like Jobs can deny it now.
Plus there's the issue of time: If you have 100+million to throw at something and get it right now(in 6 months after due diligence), or spend the 100 mil on an in house project, wait 3 years, and get it then...which would you take? Personally, if I had that kind of money to throw around, I'd want it now, so I can start implementing my vision now. Don't take the numbers here too literally, 3 years might only be 1 year…
Why would Apple (or any other OS company) be in a hurry to get this product?