Adding to that, when iTunes came out, most people didn't put any thought into ID3 tags. When they imported their music, their library became one big mess.
So much for ease of use for end users.
The thing was iTunes wasn't designed to be a music loader, it's a music manager. This became evident when they introduced smart playlists.
A few of my friends had Nomads, they were large, heavy and the UI was archaic in comparison.
This is back when you had to figure out which Mp3 encoder you wanted to use.
Why can't the iPod work without iTunes? (It can, but only with a lot of work.)
Oh and anything that involves the file system is not friendly for a surprisingly huge number of users.
"User friendliness" in this case also includes developers, who could easily write a program that interacts with the device. For example, any media player could be used to synchronize music (if it supports that feature).