i just found out that the songs purchased from itunes is just a rental

You don't own the music on a CD or the video on a DVD either. When you watch a DVD, you'll notice the note of something like "this is only for private viewing". What you actually have is a license to watch the movie, in private. If you tried to host a commercial viewing, that is illegal.

In either case - CD or iTunes - you're only buying a license to listen to the music.

 

You can redownload itunes music and it's also DRM free. Really there's nothing keeping you from moving the songs to an external hard drive for storage.