While there are certainly strategic considerations involved in Apple's acquisition of P.A. Semi, for Apple they would never quite amount to a sufficient reason to go ahead with the deal without being combined with a more intangible factor, which might be described as compatibility or affinity.
To put it simply, Apple must see a lot to like in P.A. Semi, and for its part, P.A. Semi found Apple's overture welcome.
This wouldn't be so much about specific technologies as about corporate culture and the sheer competence of the people who make up the company, and whether those people anticipate becoming engaged or even enchanted with what they'll be doing following the acquisition.
So take all speculation based in strategic theories with a grain of salt, and join me in relishing the moment with a twinkle of delight.