Actually, the delete thing goes back to the original mac os heritage. Originally, you could eject a disk without unmounting it, which was deliberately designed to work that way. Dragging it to the trash was Apple's shortcut to unmount and eject at the same time. Its no longer in effect in that manner but the basic interface mechanism remains because Apple wont remove a predictable behavior, ie, people expect this from a mac now, and so they leave it in there.
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Actually, the delete thing goes back to the original mac os heritage. Originally, you could eject a disk without unmounting it, which was deliberately designed to work that way. Dragging it to the trash was Apple's shortcut to unmount and eject at the same time. Its no longer in effect in that manner but the basic interface mechanism remains because Apple wont remove a predictable behavior, ie, people expect this from a mac now, and so they leave it in there.