I am going to add some comments regarding why more time creates a stabler tank, and is more suited for delicate creatures. When you first cycle the tank all you are creating is the bacteria necessary to support your tank. This is important as it removes ammonia, nitrite, etc... However, it is only one cog in the biological filter. You also need worms and pods to break down detritus. This helps your tank deal with added food and critters better. You also need time to build diversity in the population. If something varies your system will react better since it may only impact one portion of the population. I set up a tank and let it run for three years. I broke it down and took a break. I then set up another tank recently, and it has been up for about 9 months. I have already gotten burned, because bad habits I developed that were okay with a three year old tank do not work on a much younger tank. The system just isn't developed enough to cope with my mistakes yet. The last two reasons an older tank is more stable have little to do with the tank and apply more towards the owner. With time you understand exactly what your tanks need. You know approximately how much evaporation you get, how much calcium consumption, and alkalinity needs your tank has. You know how much food is required, what is too much and what is too little. You in sense calibrate to the tank so that your day to day feedings, additions, and maintenance cause the least amount of variation. The last main item is equipment/design issues. You may have completely thought out your design, however most tank "disasters" happen in the first few months. You cook the tank because the heater set up had a failure method you didn't foresee. It took a couple months for the opportunity to present itself, but eventually it did but it cost you some livestock. You overdose water because the fail-safe auto-top off you installed failed. There are inumberable little design flaws in most set-ups. It takes about 6 months for most people to flush these things out of their system.
I hope this helps explain some of the slow down comments everyone is saying and starts to explain how an older set up is better for delicate creatures. I am the same as you in that I need to know all the why's for doing things. Hopefully this helps explain some of them.
-chris