Earlier quoted context omitted.
There's a difference between 200 million new files and 200 million 'uploaded' files. eg a song has a fingerprint. If 100 other users 'upload' the same song, it's counted towards their usage but no actual upload or storage is performed, saving costs. Pretty clever on their part :)
Yes it is very clever, I had forgotten they ensure they only store unique files (I wonder what percentage of files "saved" are unique). I actually went and looked through the TechCrunch articles from April 17th that announced the Dropbox 25m user mark and 200 million file saves but it doesn't distinguish between unique and saved files. I imagine its the latter as it would be the more impressive number. http://techcru…
I.e. bigger files are more likely to be stuff that you didn't make yourself.