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The DSi was an upgrade to the DS but not a whole new console generation.
The Wii Mini was a downgrade (seriously) to the Wii to make it cheaper/smaller.
The New 3DS was an upgrade to the 3DS similar to the DS->DSi upgrade.
Plus all of the Gameboy and Gameboy Advance models which you could argue were often more revisions with some new features but still compatible than a totally new product.
Such as the Gameboy SP and then Micro which were totally new designs for the Gameboy Advance with a better screen but otherwise the same console.