I'm all for pushing as many pixels as we can, but not at the expense of battery life. I'll happily take a 720p screen if it buys me even a mediocre improvement in battery life.
You'll find people saying this all the time, but you'll also find that it's mostly based on armchair reasoning. I'm willing to accept that higher resolution => higher GPU usage => battery usage increase, but I'm not willing to accept that this has a significant impact, not on face value. Not considering that the GPU is only heavily used in short bursts for all tasks that are not gaming, and considering that its power drain is likely still insignificant when compared to the power usage of the backlight.
A year or two ago you could compare the HTC One M7 and the Nexus 4. Two phones with very similar internals and screen size, but the HTC has a 1080p screen and was usually reviewed to have a slightly longer battery life.
But a larger screen won't necessarily require much more computation. Imagine showing photos, for example. The increased size of the memory copy (from disk to RAM to GPU), won't consume much more power, I would think.
And if it does, it will only be when loading the image to show it on the screen. After this is over, it will sit idle until loading the next image (consuming no additional power from use of CPU/GPU/storage).
For games, though, you're right. A higher resolution display will make a larger difference in CPU/GPU/storage power use, especially if the CPU is used, since the GPU is probably designed for a higher resolution display.
so everything else equal you already have a higher idle current drain from the SOC side whenever screen is powered up.
Yet we use smartphones...
Anyhow, my Nexus 5 lasts the day, I plug it in at night. That's good enough. And I like the screen.
Battery life only matters to a point - after that features and niceties matter more...
Second, there is such thing as a 'good enough' battery. For most people, this has been achieved with the current crop of big screen, high res phones.
Not sure why you think people would accept lower resolution for an extra half hour of battery life...
I agree that we are at a time when battery life should be prioritized, but I would prefer that to come from thickness. Increasing the thickness by just 25% or so would allow a much larger battery.
Obviously there's a cost to this, both in battery and hardware requirements to push those extra pixels. Meanwhile nobody can detect pixels on a Nexus 5, but apparently it wasn't good enough.
And next year we'll see PPI at 500-600. I just don't get it.
As for thickness, I think the Nexus does quite well. It's about 50% thicker than the iPhone 6 which is a great number (~10mm) to be at in my opinion.