The key in this argument is P.A. Semi make industry leading low-power chips, and also founder Dan Dobberpuhl was a designer on the StrongARM project which, among many other things, produced the CPU for the Newton. Apple use ARM in all their portable devices currently and also by that virtue have a OS X ARM branch (the iPhone/iTouch version). Purchasing P.A. Semi would give them a chip design team on staff to design custom chips for these devices without having to outsource. P.A. Semi have no fab facilities so Apple aren't going into chip manufacture, they just want their own designs and found a convenient way to find the staff and expertise to do it. P.A. Semi only employ approx. 150 people so it's not exactly a huge leap.