You will find out in brewing, just like life, that there is more than one way to skin a cat, nor is there a "better" way...the only way is the one that works for YOU as the brewer.
We say that if you ask 10 homebrewers a question, you will get 12 different answers...and all of them will be right.
As an author I have found that it is the same...when we write books, or articles, or teach classes,
we do it based on how WE prefer to do whatever it is that we are writing about. And we come up with hopefully great explanations to back up why.
I'm sure he believes it is necessary and rationizes it well...and he may simply be doing it that way because that was how he was taught, or he did it ONCE and was successful, and has never tried it differently.
I've mmade starters and never added any, and guess what? It works for me, just like his way works for him. *shrug*
So just because "so and so" does it that way, doesn't mean that another brewer or another author doesn't have a different take....
and I have come to realize that ultimately, they all achieve the same goal...making beer. Or in your case a starter.
The best advice I can give you,
Is to try it different ways as you brew, and decide for yourself ultimately what works for you.