In response to rampant pirates that tweak the x86 (Intel) version of OS X's kernel to get OS X to run on ordinary PCs, Apple will no longer be offering the source code to this kernel. However, there is another side to offering the kernel to the public. Many advanced users will modify the kernel to optimize OS X for the specific application they primarily use OS X for. Macworld UK argues that this is a bad strategy on Apple's part and might cripple their hardware sales for new products like high-performance servers where consumers generally slim down the kernel to provide for breakneck speed instead of the broad compatibility that the kernel was previously optimized for.
Apple will still be offering the kernel source code for PPC OS X. Apple needs to decide what they want to do in this situation. They might be able to put a cap on pirated software but they will upset developers in the process.