I think what needs to be kept in mind is that the definition of mastering has changed over time. Whereas back in the old days, mastering only meant making the songs in an album or collection sound good together, now it has shifted quite a bit. Of course, mastering has kept that old definition, but now it's more aimed to increase sound quality and to avoid listening fatigue. In my opinion (maybe not in Mat Zo's) I believe it's important to have at least some sort of basic mastering techniques that you do for each of your productions (be it a basic mastering channel or a step by step process to master your bounced file.) You will see that as you practice mixing and mastering more and more, your productions will be of higher quality in less time. Not only this, but keep in mind that mastering also requires a certain ear that can be developed with experience and time. Practice it and it will help you a lot!