There's an explanation here of why different chargers do indeed make a difference:
see in particular the note on the Battery Charger Spec.
In particular. my own testing shows I can go from 500ma to 700mA charging current simply by changing a small connector in line between the 7Ahr battery I'm using to charge the phone, and the phone. That's due to the nature of the short on the data pins.
There are proprietary tweaks to this mechanism; e.g. iPhones use voltage signalling between the two data lines and ground to indicate various things to the device.
All of this is only for "hosts", i.e. chargers etc, that don't implement the USB protocol and so can't engage in the normal current negotation that occurs when connecting e.g. the device to a PC.