Faster processors run at higher voltages and the relationship between voltage and power consumption isn't linear it's squared, i.e. a 1GHz processor doesn't use twice as much energy as a 500MHz processor, it uses four times as much. You can mitigate this increased power consumption by going multicore, i.e if you have a 2 x 500MHz dual core processor you are only using twice the power not four times as much. Because multicore processors can do multiple things concurrently you get back to reduced power mode quicker too. This is why we are seeing more and more cores being used. The Lumia 720 had a 1GHz dual core processor whereas the N9 had a 1GHz single core processor. On top of that the N9 only had a 1450 mAh battery whereas the 720 had a 2000 mAh battery. It's really quite logical the battery life of the 720 was around twice that of the N9. It had nothing to do with the OS. Therefore the mystery forum member's 'deciding factors' were entirely to do with NOKIA's hardware improvements between June 2011 and February 2013. Of course they could have made these improvements even sooner but they had to wait an eternity for WP to get multicore support. Do you remember that now, Lumiaman? Do you remember the stupid things Elop used to say about multicore processors back in the days Windows Phone didn't support them? He's not saying it now is he?