Getting customer data into your system is harder than it looks. Flash uploaders are pretty crappy, but you need them for IE users and direct to S3. Flash is broken for mobile, of course, as is the whole 'upload from computer' concept. Box, DropBox, Google Drive, flickr, and everything else is extremely popular, so if you start implementing all those yourself it adds significant development time and code to maintain. Filepicker has been a huge win for us at PlanGrid.