Here's Nintendo's DS family beginning in 2004:
Nintendo DS Lite
Nintendo DSi XL
Nintendo 3DS XL
Nintendo use the same naming scheme (adding one or two letters as a suffix or a prefix) for revisions and successor systems. That's what causes the confusion. I can completely understand why many people thought that the 3DS was just a 3D version of the DS after the DS Lite, DSi, and DSi XL.