Wii is not next-gen, is this-gen (Can we please eliminate this "next-gen" phrase from current generation systems, English is my 2nd language and even i can tell that this combination of two words is misused)...
Now, talking about generations, i can go back to the NES, when they started the 3rd gen, we knew it as "The late 8-bit era", then the Genesis and the Super NES led the 4th gen, or "the 16-bit era", then the 5th generation started when the Saturn and the Playstation came out with 32-bit chips and then the N64 came out with a 64-bit processor, does Nintendo skipped a generation??? Hell no. Was everyone saying that the Playstation and Saturn were last-gen??? Hell no...
Now, back to this gen, graphically the PS3 and the 360 are superior than the Wii that's true. But the Wii has the motion controller, the PS3 has it but not at the Wii range, and the 360 doesn't have it at all. PS3 has Blu-Ray, 360 and Wii still use DVDs. Wii has no hard drive, 360 has it but is not mandatory, the PS3 has it mandatory. Everyone of them have online stores and unified networks. Everyone of them have wireless controllers. Two are white and one is black. All of them stand vertically or horizontally. All of them connect cables to the TV... Can you see where i'm going here???
Generations are not measured by graphics, sound, storage, controllers, processors, etc., generations are when the consoles come out...