Switching to a PC won't get rid of the vendor lockin with Nvidia with some third party apps. You will still continued to get kicked in the nuts by Nvidia.
I dont care so much about a vendor lock with there videocards. You know what i do care? I do care that my video renders two times faster, i do care when i can see live my effects i drop on a video before i push them to a render, i do care that my filters in Photoshop are almost realtime rendered when i drop them on a layer, i do care that my system is blazing fast. I know, you can argue about OpenCL etc.. All i know, is that my tools are asking for CUDA and openCL and that AMD is not providing this off course. That the old majority of the Mac users where creative content makers, should Apple think to at-least give you a choice. But that would be a change in the arrogant road map of Apple off-course. And i wont see that happen in the next bilion years! So, thats why i have to move, and many others all-ready did.
If you want a nice looking machine, go for a imac. If you are a FCX user, you're fine with a mac pro. If you are more power demanding with Cuda hungry tools (a lot of content creating tools), you have to think about to switch or swallow Apple and pay the premium platinum price for average. But, you have a nice shiny round computer. And.. like is said before... thats cool too!