Note: The frowning face in the title got there by accident and there doesn't seem to be any way to remove it.
I assume that part of the justification for the lack of access to the file system on the iPad is that it is intended to be a Cloud device.
Partly by intent and partly by accident I seem to be overcoming many of the perceived shortcomings by setting up my own, personal Cloud.
I have a 1TB NAS (WD "White Light") and have loaded up some apps on the iPad that allow me to manage files locally pretty much as you would with a PC or Mac.
The applications are FileBrowser, iSSH and, to some extent, WD Photo.
An example of what I can do, is to plug an SD card into my HP (ePrint) printer and copy files from there to a public NAS folder using FileBrowser. WB Photo can be used to SELECTIVELY copy photos from there to the Camera Roll.
Now I have easy access to the 25 GB of images on the file server (using FileBrowser or WD Photo) and can move selected photos onto the iPad and view them in Photos.
FileBrowser is a bit slow at copying folders and that's where iSSH comes in.
Firstly the WD NAS allows you to enable SSH (Linux scripting). Originally this was an unofficial hack, now it can be done through the WD web based management tool.
With iSSH I can use Linux commands to copy files around the the network, bypassing the iPad, hopefully achieving greater speed. I haven't actually managed to mount the SD card (in the printer) from SSH yet, but if FileBrowser can see it, it must be possible. A bonus is that I can use file specs (e.g. *.jpg) to be more selective as to which files are copied, copying jpg files to one folder and raw files to another folder, for example.
Also, WD supplies web based copy manager that can do bulk background copies at reasonable speed.
One minor annoyance is that part of the WD NAS initial set up is Flash based , but I have only had to use that once so far.