I actually just asked this same question yesterday. In general, it is a good rule for beginners to stick to, but not an absolute rule. When looking at how fully stocked, you need to consider your filter and if it will be able to keep up with the waste produced, how big your fish will get, agression, where your fish swim (top, middle, bottom), will there be enough oxygen for everyone, etc. Basically, will all your fish's needs be met.
Ok, just remember, if cycling with fish, start slowly. If you are doing a fishless cycle, go ahead and add a full load by the 1" per gallon, then wait to see how the fish are acting before adding more (do so slowly).
Sorry if I confused you. When you do a fishelss cycle, you can fully stock your tank afterwards. HOWEVER, if you are going to try to push the limit of how many fish you can have, then I would say start stocking at the 1"/gal rule, then slowly increase from there.