Sony did not decide to make their system more difficult to program for. The reality is they couldn't use hardware or software that mirrored the 360 to any degree, cuz MS would have stopped the PS3 from launch & delayed it with court battles as long as possible.
Because Microsoft have any kind of ownership over modern computer design? Oh wait, no, they don't.
Sony didn't decide to make their system more difficult to program for, that's just a side effect. Theoretically, the PS3 is quite the number cruncher - they took a gamble that people would use that to do cool things, like more complex physics or AI. They didn't.