Then where did you get the line....
yes there is circuitry inside the newer iPhones that take advantage of the additional power from the 12W charger.
That can't be "personal experience" to state there is circuitry.... Or is that purely speculative (which you probably should state if you make such a statement).
TL;DR: "my informed opinion"
By measuring the current consumed, figuring out the circuitry, and applying my engineering knowledge. There is a USB charging spec available in the industry that describes how to apply up to 2.1A @5v to charge via USB.
ASMedia is one company whose USB controllers are able to do this.
Apple devices are known to place a certain resistor value across the USB signaling lines that instruct some adapters to provide different power levels. OS X and iOS also can detect when a non-Apple charging accessory is used that does not contain the proper licensed authentication inside.
On certain Apple computers, Apple knows when specific Apple devices are connected to compatible USB ports, adjusting the available power. This started way back on the G4CUBE computer (no relation to me
). The bundled USB speakers had incredible volume because the G4CUBE could provide additional current when those particular speakers were attached.
Similarly, the Apple Superdrive requires more power than a standard USB port can provide, so Apple's Macbooks are able to deliver additional power over the USB ports when the Superdrive is connected.
There are reports of various USB chargers where people have disassembled them to figure out the specifications and power limitations, in addition to power quality. Google is your friend.
But you are correct this is my opinion, and Apple has not stated this in any public documents.
On a related note, there have been other published reports and technotes by Apple explaining that a standard USB port on some computers will not charge an iPad or an iPhone, as those ports only can supply 2.5w as power available is 5v @500ma.
And the original aluminum 15" Powerbook complained if a USB device that consumed more than 500ma was connected, and hut the port down.
So...if you have a voltmeter, a dynamic load, something to measure current, and some design skills, you too can take a peek behind the curtain and discover what capabilities Apple devices have.
Just a word of caution though, you can't always count on using hardware capabilities that are not actually guaranteed by Apple for non-Apple use. Especially on the software side, as there are many internal system APIs that Apple has not published but uses with their own applications. Developers get bit when they use them without authorization.