Consider that with the method Thirsty Boy describes you get a completely sanitised system that is guaranteed to be purged of any atmospheric oxygen. If you're filtering, that gets sanitised into the bargain. It does cost you money, but so does almost everything you do as part of brewing. I guess it is up to the individual brewer to decide if it is a reasonable expense for them.
Kegged beer is for drinking at my house, so I don't bother. But I do so with the filtering unit if I am using it and on special occasions - such as if I am going to take it to a party or something. But, it also goes into the fridge almost as soon as it has been filled, so although it has probably absorbed some oxygen, the effects will be slowed - hopefully enough that it isn't noticed until after the last glass is drained.
If I am naturally carbonating in any sized vessel, I would have thought that doing so with yeast in their anaerobic state is best and therefore reducing available atmospheric oxygen remains a good idea.
Clearly what is needed is to make the brewery completely air-tight but for a small PRV in the roof/ceiling so the CO2 produced by fermentation expels all other gas in the brewery. The brewer then simply needs to don a small aqualung to safely conduct any packaging tasks. :lol: