Don't worry, you still can't copy music from a device back into iTunes. I mean, obviously the bits representing the music flow from the iDevice into the computer, but the computer doesn't belong to you anymore, so you don't get access to them. Silly user.
USB devices fail in that they rely on the user to make his own decisions about whether or not to copy his friend's music collection. Apple devices let some music execs representing bands I've never heard of make them for you instead.
USB mass storage players also fail nicely at being usable for most normal people. Plug it in, get an Explorer window, now what? Open another Explorer window -- reposition windows so you can see both. Navigate to your music collection. Find the first thing you want to copy -- hopefully your music folder is well organized by filename. Copy (don't move!) files. Make sure there are no incompatible filenames. FAT32 isn't very forgiving about this. When you're done make sure you safely unmount the volume by right clicking on the green arrow in your system tray (the thing by the clock). If you have multiple green arrows just try right clicking on them all until you find the right one. Now enjoy your music and start preparing to repeat the process tomorrow when you want to add a song.
At least you have the option, and the device doesn't go out of its way to make life difficult for you and any software that tries to access it.
People love to think that users are completely clueless, but it's not the case. The general user has absolutely no problem using a USB drive. Sure, it might not the most usable option but it's not as arduous as you describe.
And organised music folders? Either it matters, and you play music directly with Winamp (or similar), or it doesn't matter at all and you use a jukebox program that works with the tags. You can also just play music straight off the drive if you want - fairly common in my experience.
I've been using iTunes since version 3, and I don't think I've ever seen it treat a mass-storage player like an iPod. There was, however, until perhaps very recently, vestigial support for a handful of very dated mass-storage players, a strangely-untouched holdover from SoundJam MP. I never did see what would happen when one of those was plugged in.
There is nothing intrinsic about USB mass storage in that experience.You can make an iTunes like experience based on USB mass storage drivers, Apple has chosen not to for other reasons.
<responding to troll> though of course you can copy music off an ipod by copying the mp3 files off it like any other mounted disk, except that they are in a folder with its hidden attribute set.
You'll need a different hack to put music or video files from a random computer onto your device too. That's assuming it's even possible, they seem to be in an arms race each new devices having your data further encrypted in some way.
I've got around this in the past by importing the bizarrely named files into iTunes and then telling it to automatically organise my library for me. It then uses the metadata in the mp3s to rename the files back to how they should be. Not sure if it still does that these days.
You don't have to use iTunes, or even an Apple app, to get things on and off an iDevice. For example: http://ecamm.com/mac/phoneview/
Blurb:
Multimedia Is No Longer Trapped on your iPhone, iPad or iPod Touch
Free your Photos and Movies -- Download camera photos and movies in just a few clicks. You can even use PhoneView to export the iPhone's synced Photo Library if you've lost the originals.
Music Made Easy -- Play any iPhone, iPad or iPod Touch music library through your Mac's speakers. Grab music, videos and podcasts from your device with one click.
Frankly, I have one that mounts as a USB drive and one that is an iPod, and I much prefer the iPod. Real sync capabilities make all the difference to me, and WMP sync is annoying, buggy, and slow.
USB devices fail in that they rely on the user to make his own decisions about whether or not to copy his friend's music collection. Apple devices let some music execs representing bands I've never heard of make them for you instead.