Aslong as theres a filter agitating the surface theres no need for it but it wont do any harm leaving it on so its up to you.
Actually, you can slightly oversaturate water with oxygen -- especially if the water is cool and being warmed up (like just after a water change, for example).
It is unlikely, but it is possible to get oxygen to too high of a level that it could be deadly -- kind of like hoe humans cannot breath pure oxygen gas.
Nonetheless, your main point here remains true, in that a tank with an agitated surface will almost always be at equilibrium with the atmosphere anyway. Injection of oxygen is unnecessary. Fish have survived and thrived in tanks for a very long time without oxygen injection. Someone sold you something that isn't really needed at all.
And then, unless you are going for a lushly planted tank, there isn't really much reason for the CO2, either. Maybe if you were going to attempt to breed fish and needed to achieve a perfect pH. Otherwise, the CO2 isn't needed either for the vast majority of tanks. And, yes, you can have lushly planted tanks without CO2, too.
What are the plans for the tank? That may help a lot to determine how needed the gas injection system(s) will be.
/www.aquavistainc.com/products_wallmounted_panoramic.html
