The real weakness of Intel in power consumption relative to ARM hasn't been so much in the chips as the chip sets, software and the balance-of-system.
To create a low power system, ALL components need to be low power, and it is easier to start from a system built to be low power and scale up capabilities rather than go the other way around.
For instance, I have a Windows-based laptop which is a great machine, but if I have a web browser open, any web browser, the fan spins, it gets hot, and battery life is less than 1.5 hours.
Is it the fault of Windows, the browser vendors, the web platform, adware, crapware, who knows what? It doesn't matter, but controlling power consumption on a legacy platform is a game of whac-a-mole that doesn't end.
Because Windows users expect to plug in devices that draw power from USB, a Windows tablet has to have a huge power transistor to regulate voltage, a power supply system scaled up so it can supply enough power through the USB port to charge an Android tablet, at this point you might add the fan and then you are doomed.
The x86 instruction baggage is a red-herring. It takes maybe 3% of the transistor budget to support it.
I saw an interesting interview once with an ARM exec who leveled and said they don't really have a big power advantage over Intel, despite what people commonly think. I didn't manage to find the article with Google though.
To me it seems mostly a problem of unwalled garden. When Apple owns the platform from the silicon to the development environment, it's easier for them to manage power. Wintel on the other hand has so much variety all the way down the software stack and even into hardware, it is more difficult to control... x86+Linux (Lintel?) suffers the same problem.
The unwalled garden can still be made low power. Android has set an example of tackling that problem with the battery tracker, which profiles which application is chewing up battery.
For power over USB, what do you mean? My Android cell phone can power keyboards, flash drives, and the like with an OTG cable. It certainly has no fan.
Wikipedia says: "A closed platform, walled garden or closed ecosystem[1][2] is a software system where the carrier or service provider has control over applications, content, and media, and restricts convenient access to non-approved applications or content."
Google doesn't restrict access to applications or content on my Nexus 5, so how is it a walled garden?
Which may appeal to you as a developer, but from a user perspective, that isn't a good thing.
Consider this analogy: Would you buy an "open-source" deadbolt for your house? Great feature for aspiring locksmiths! But very likely not such a great feature for 99.9% of home owners.
To create a low power system, ALL components need to be low power, and it is easier to start from a system built to be low power and scale up capabilities rather than go the other way around.
For instance, I have a Windows-based laptop which is a great machine, but if I have a web browser open, any web browser, the fan spins, it gets hot, and battery life is less than 1.5 hours.
Is it the fault of Windows, the browser vendors, the web platform, adware, crapware, who knows what? It doesn't matter, but controlling power consumption on a legacy platform is a game of whac-a-mole that doesn't end.
Because Windows users expect to plug in devices that draw power from USB, a Windows tablet has to have a huge power transistor to regulate voltage, a power supply system scaled up so it can supply enough power through the USB port to charge an Android tablet, at this point you might add the fan and then you are doomed.