Good ideas come from both sides, and then are embraced, extended, etc.
The problems arise if the two products start to diverge, and if application developers have to make decisions about which of the two systems they target their products at. Given the size of the Linux market it would be madness to choose more than one. Ideally I would be able to run the same application on either system. At the very least I demand interoperability at the file level. All they are interested in is getting the job done.