Hay,
I think it depends on the AVR your using. My friend has an older Pioneer and does it just like you said by placing the left main at 0dB and adjusting the main volume until he reaches 75dB. Then he cycles through the rest of the speakers and adjusts those.
I don't believe I'm able to calibrate in this same way with my Denon as the test tones are locked at a certain volume level. I can either run the built in setup with microphone, or use an SPL meter and cycle through each speaker and manually set them to 75dB's or whatever. Sometimes I do both. I have found the built in setup does a very good job.
You are correct though, as many people follow your method if possible. This is explained on many reputable AV websites.
