The difference is that on Android you have complete access to the file system but on iOS you don't. My interest is to be able to back up photos from my camera's SD card while travelling.
With iOS you plug the SD card in via the Camera Connection Kit and the files are automatically copied to the Camera Roll, internal memory only. JPEGs are visible but RAW files are not. I think that iOS is smart enough to copy only new files the next time. I think also that these days, files (JPEG & RAW) can be copied off Camera Roll using the host computer's file manager when the iPad is connected via USB.
On my Andoid phone I can plug in a 32 GB Micro SD card and create folders as I like, usually one per subject with subdirectories for JPEG and RAW. I can plug in a mini SD card reader via USB and use a file manager to select and copy first JPEGS, to one destination then RAW files to another. I am asked whether to replace existing files or not.
Perhaps I am being inflexible, but Android definitely suits my workflow better.