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I feel that this question could potentially have more specific and direct sub questions but for now I would like to simply pose it as "why not oxygenate active yeast prior to pitching instead of oxygenating the entire batch?"

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Strictly speaking, as long as you can ensure adequate and even oxygen contact with all of the yeast cells (a hard task, given the viscosity of yeast slurry), and provided the oxygenation comes directly before pitching, oxygenating the yeast/slurry itself is completely sufficient to provide for adequate growth in the following phase. Even more strictly speaking, it is, in fact, beneficial since it largely precludes the possibility of oxidizing wort components, which could lead to staling flavors and haze instability over time.

This exact question has been posed in serious brewing literature before, e.g.:

"Oxygen to yeast or to wort? Oxygen is added to the wort as a nutrient for the yeast. There is some reaction of oxygen with wort constituents and some believe that this is not only wasteful but also detrimental to the flavor stability of beer. Accordingly, it has been argued that it makes more sense to oxygenate the yeast immediately before pitching per se, rather than the wort. Provided the physical challenges inherent in trying to get oxygen to all of the cells in a thick slurry are overcome, it is certainly the case that improved fermentation control can be achieved by pitching defined quantities of oxygenated yeast."

Pulled from this book.

However, I don't know of any commercial breweries using this practice. I've only ever seen direct wort oxygenation/aeration, even on the most modern and technologically well-equipped plants. This means that, while it's completely possible and biochemically sound, it's probably way harder to do practically than is worthwhile, especially given how easy it is to properly oxygenate wort. It's just one of those odd cases where it may technically be better, but the difficulties in doing it simply outweigh the benefits.

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There's only so much oxygen that the N-hundred billion cells that you pitch can "hold". As well, there's only so much oxygen that can be diffused into the liquid containing those cells. And not only will those pitched cells need more oxygen, but their offspring cells will need oxygen, as well. As such, we oxygenate the wort, not just the pitch.

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    There is some evidence that simply aerating the starter is all that is necessary and that if you do that you don't need to aerate the wort. However, as homebrewers our procedures aren't perfect so it's safer to aerate the wort also. Also, there isn't really a separate lag phase. According to the Crabtree Effect, fermentation begins immediately in the presence of a >.5% glucose solution, which wort certainly is. So fermentation and yeast growth happens simultaneously. – Denny Conn Jul 6 '15 at 17:23
  • I absolutely agree @DennyConn with your view on yeast phases. I am a student of the White and Zainasheff book and thats where the question come from. Rereading today for the zillionth time, page 66 paragraph 5 refers to cells needing oxygen in the lag phase to create sterols (amongst other things) which is critical for cell membrane permeability. So my thought is oxygenate the the yeast prior to pitch = safer more protected yeast... but the simple fact that all the cells aren't on the same "phase" at the same time answers the question. – Ryan Shdo Jul 6 '15 at 18:30
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    @Denny Conn, I think your comment should be answer. – Pepi Jul 7 '15 at 6:58
  • Ryan, you're overthinking this. It really doesn't matter what "phase" the yeast are in. – Denny Conn Jul 8 '15 at 15:43

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