No offense but I dont really understand how there is an exception to the rule. Honestly I dont.
None taken... :)
The reason why I said exceptions to the rules, is because this hobby is nothing more than science, and in science, there is trial and error. The hobbyist/scientist before us had their trials and errors, which pretty much became the rule of thumbs. But in science, there is advancement, and evolutions, and new found studies. For example, we teach the "one fish per 10 gal rule. This is great advice, to the common hobbyist, and the newcomer, but to some, with adequate planning, you can make an exception to this rule. I've personally done this myself, and have 7 fish in my 37gal mixed reef, with perfect parameters, maybe because I have over 100 lbs of rock. :)
Another one is that all anemones need mh lights, a good buddy of mine has a tank of them with only pc's...don't ask me how he did it, but his tank i's awesome and thriving. I don't recommend people breaking the "rules", but if you've done your research, and have the experience, then making an exception to the rules can prove rewarding. Now, a pair of clownfish in a 3gal, that's really pushing the limits, but I'm sure there is a reason behind his/her decision.