Not entirely true or false. DOC's are generally addressed in nature by a complete ecosystem. In an aquaponics setup items other than those not used for plant life don't generally get to a point where they need to be addressed by water changes. This is not to say water changes might not sometimes be warranted, however they can also be detrimental depending on the setup or usage you have. In a setup inside the home where bio-loads may not be fully addressed by plant and or bio filters regular water changes may be quite appropriate. In a full fledged aquaponics system the plants require the "food" load and thus the system is "loaded" to address the plants needs. A healthy system requires a balanced load... plants however can compensate for a low load or deficient load. A system I am currently assisting with has been running non stop for 5 years without a water change, water is only added.. the plants and fish are all extremely healthy and have both been used as food for the entire life cycle of the system. The hardest part is when the plants or fish are harvested, at that point balance is hard to maintain.
So, like i was saying, in home systems where this balance is harder to maintain due to bio load or plant filtration it may be quite advisable to do water changes. Since most of the readers of this thread are focused on ornamental style plants you advice may be even more valid. If however people are going to teh more extreme measure of say a full on aquaponics system the info provided here is only the tip of the iceberg.