Generation is dependent on when it arrived. Nintendo is launching first, so they're the first of the next generation - Wii launched after Xbox 360, and at the same time as PS3, they're the same generation. Unless PS4 launches around the time of the Wii U successor and Xbox 4, it will be the same generation as the 720 and Wii U. Generation has nothing to do with power at all - it's timing, and typically revolves around the leading company - which as of this generation and 250 million hardware units sold between Wii and DS, is Nintendo.
No one in their right mind would argue that the Atari Jaguar and N64 were a generation ahead of PSX because they were 64-bit while the PSX was only 32-bit.
To run another perspective:
Despite Arnold Schwarzenegger being much more powerful than David Bowie, they're still of the same generation.
Despite Katherine Schwarzenegger and Patrick Shriver being much less powerful than Arnold Schwarzenegger, they are still his children, and therefore the next generation.
I describe myself as a little dose of toxic masculinity.
