Firstly the PS3 situation was never quite so low as the WiiU's and as someone already said there is only so much you can turn around.
My answer's are as follows.
1. The parity between the PS3 and 360 meant that developers making games for the 360 had little to lose by also porting to the PS3, even when sales were poor. This kept third party support alive when it could be argued that it wasn't truly deserved (on the basis of sales, momentum, prospects and development ease)
2. RROD: served to somewhat stall the 360's momentum and cast the PS3 in a more positive light.
3. Price drop: the initial price was silly, it really needed to be cheaper and it happened.
4. Sony's first party started performing when they needed to.
All four together allowe the turnaround to occur. Nintendo have been addressing 4 but have much less incentive and room to move on 3. 1 and 2 were happy accidents so can't really be replicated.
