Drag n Drop Songs to an Ipod

I am figuring if I wan to get an iPod and I need to confirm this once and for all with people who own iPods.

When you wan to transfer songs to your iPod to listen to, can you just plug the iPod to your PC, and drag-drop mp3s into it?

Or do u HAVE to use iTunes to tranfer the music?

I thought so.

SO WHY did Apple decide that we HAVE to use iTunes to tranfer songs? What is so wrong wit just dragging and dropping mp3s to it? Isnt that more user friendly?