[kens]

I took a look at the LM323 datasheets out of curiosity. As with the 7805, there are multiple designs that are very different. ST Microelectronics' LM323 has almost the same circuit as the LM109/7805, with a bandgap reference. Motorola's LM323 is similar to the LM340, with a Zener reference and a comparator. So you have two LM323 chips that use not just different circuits but fundamentally different physics to regulate the voltage!

As for how the LM323 supports 3 amps, the datasheet attributes it to "new circuit design and processing techniques". I'm tempted to open one up and see what's different from the 7805 (I'm guessing a bigger output transistor), but I've already got too many chips I want to look at.