No, you can generate 'regulated' DC from another DC source (see for example buck converters or more generally any DC-DC converter).
Regulated really just means clean DC which stays at the same voltage and doesn't contain a lot of noise. Not all devices require a regulated supply. A drill, torch or heater will happily run on a noisy supply. Your iPhone will not.
You are right. I remember more details now. The problem occurs when you want to make regulated DC from a lower voltage DC supply. Step-down is easy.
For example, my battery is 12V, but my laptop needs 19V. AFAIK, you can't get regulated 19V supply from the 12v battery without a transformer (or maybe something equivalent).
Step-up is easy too. That's what boost converters (http://en.wikipedia.org/wiki/Boost_converter) are for. Most single-cell LED flashlights contain tiny boost converters to increase the 1.5v coming from the battery to above the drop voltage of the LED.
Regulated really just means clean DC which stays at the same voltage and doesn't contain a lot of noise. Not all devices require a regulated supply. A drill, torch or heater will happily run on a noisy supply. Your iPhone will not.