Umm, if it's on your dropbox or other filesystem you can use it on your iPad, no?
You see, I can USB-plug almost any Android device into any Windows or Linux machine, and transfer any files either way without installing any software. It just works.
Even with Dropbox, what if it's a 10GB file? Are you going to upload and then download it? Do you not see how ridiculous that is?
I don't, but it sounds like my use case is different from yours, so I guess what seems absurd to you is normal to me and vice versa.