Yep, that seems key. I've just spend full 5 days (I'm in between contracts, so I have the time) trying to install Arch on my Early 2013 15" MacbookPro. I turned out that, due to buggy/nonstandard hardware, a fully functional dual boot with Windows is not possible (if your disk is GPT, you won't have sound on Windows and if it's MBR, the DisplayPort monitor won't come back from suspend on Arch). Just coming to that conclusion took around 4 days of experiments. I've spend one more day trying to set up wireless, and have just given up. There are more interesting things to do with computers than finding workarounds for a minefield of hardware/firmware/drivers bugs.