if you are doing a 50% change weekly, then you have theoretically turned the tank water over twice in a month. if you are only doing 10% changes, then you barely change half the water in a month. doing large water changes weekly keeps the tank water much closer in composition to the tap water so that the changes are LESS drastic. if you only do 10% a week, or worse, 30% maybe once a month, old tank syndrome is going to creep up pretty fast.
do you know anything about cycling a tank and maintaining proper water quality, Tigris? water changes are a necessary part of it to remove the final waste product, nitrates. you can't "create a natural biosphere" unless you have a heavy planted tank and a very low bioload. otherwise, organic wastes build up and will slowly poison the fish. the bacterial colonies are not disturbed by water changes when done correctly, and neither are fish. while 10g tanks may not be ideal for most kinds of fish, it's better to keep them in a healthy and clean environment rather than a dirty and polluted one.