No, it isn't a fad. Most people feel it's a fad because it's supposed to behave like one; that's the disruption model. What made the Wii successful and arguably a failure is its Blue Ocean strategy. It created a market for Nintendo, but it divided the audience, and confused the third parties. It also didn't help that most people deemed Wii failure from the get-go. Confidence was never there for third parties, but they wanted to take advantage of its market share so they developed these half-assed games that were supposed to be 'AAA' games and ended up not selling well. It's a slap to Wii owners, and an excuse for third parties to abandon the Wii.
Ultimately, what slowed the Wii sales down was Nintendo. It felt like to me that they knew they could never acquire a full commitment to third parties so they focused for the next gen: 3DS, and Wii U, and with their 7th gen profit, this gave Nintendo a jumpstart.
IMO, 3DS felt like Nintendo had similar strategy as they had with the Wii. This time, though, they think DS had strong enough brand recognition for them to sell it at $250.00 with 3D but they were obviously proven wrong.
Either that or Nintendo planned it that way to drop the price by the release of Vita... I can't prove it though. It just feels like it.
$250!