I think using the same melodic material helps to reinforce this dark energy coming from this sonata. Even before I watched these lectures, I never noticed any of the same themes repeating itself over so many times in this music, and this proves how much resources Beethoven has to disguise the little motifs. I think using the 4-note-motif adds additional suspense, and prepares the movement needs for any sudden outbursts of rage, anger, etc.
I guess some people might find this predictable, once they know that it's repeated motifs and themes entirely through the first movement, but the way Beethoven uses them inside his music really changes the way we look at it... and also proves the point that we should listen to the Appasionata with 'open ears', as Mr. Biss said.
Also, thank you to coursera, Curtis, and Mr. Biss for bringing these lectures to us, it really changed the way I look at Beethoven's sonatas. I'm usually the person who plays pieces through without giving much thought to why composers used such phrases in different places, so these lectures gave me a greater understanding of both Beethoven and his sonatas, and made me see how truly great Beethoven is.