I agree, data is not the only thing that matters; context matters too. For example, the PS3's surprisingly slow start in 2006 was at least marginally ameliorated by the fact that we already knew MGSIV was coming, that GTA IV was coming, that FFXIII was coming, that Call of Duty was coming.
Similarly, one of the primary reasons people were less concerned with the 3DS' slow start in comparison to the Vita's slow start is that we knew the 3DS had big games coming. Pokemon was coming; Monster Hunter was coming; Mario Kart was coming; New Super Mario Brothers was coming.
So if we have reason to expect large games on the horizon, then a slower start can be partially remedied. Keep in mind that neither the PS3 nor the 3DS completely solved their problems; as I said, the Playstation 3 is still the worst financial disaster in console history, and the 3DS is still significantly underperforming the DS in both the EU and the US.
The Wii U is much closer to the Vita than it is the PS3/3DS, though; like the Vita, there aren't many pattern-changing games on the way. Pokemon is not coming. Monster Hunter is coming but the console versions are much less important. NSMB has already come and gone to little effect. Wii Sports has not been replicated. Wii Fit is coming but expectations appear much lower.
In short, there isn't a gigantic wave of big games on the horizon for the Wii U. We're not hearing a lot of Wii U projects getting started up from developers on GAF (in fact, I've only heard of Wii U projects being cancelled). The context makes Wii U's prospects seem worse to me, not better. But again, even in the cases where platforms managed to "turn it around", the turnaround hasn't represented great success, it was just better than it could have been.