I don't recall having any problems getting my iPods (a shuffle, and an old mini I 'inherited' from DD) recognized by iTunes (it does get more complex to understand if you have multiple accounts and/or devices on one computer or across several computers. And, iTunes does offer some nice advantages over the drag/drop method (play counts and where you were in a track and other data is synced between them). But I'm far from a 'devout worshiper' of iTunes.
But I do agree with you, that iPods/iPads should offer drag/drop as an option. I love the fact that USB has these standard modes that you can rely on regardless of OS and what software you may have installed. That means you always have a very simple/reliable method to get something done.