Of course, it helps inventory control when you can pretty well assure yourself of a steady stream of processors. Last year, Verizon had the HTC Droid Incredible on back order due to a lack of inventory of the Samsung produced AMOLED display. HTC had to switch to a Super LCD glass. Samsung could simply not produce enough of the material to cover both it's own Galaxy S line and third party handsets.
So while it might surprise some that Samsung would choose to go with its own home grown Orion chips, history has shown that the Korean based firm has done very well by eating its own cooking. Besides, there is the prestige of making the first device to run the Orion line of dual-core chips.