Apple makes both the OS and the UEFI implementation for their hardware. If the UEFI implementation caused any trouble for OS X, they could fix it before shipping the hardware. They also use a non-standard EFI implementation (IIRC the EFI partitions are HFS+ rather than FAT; whoever thought it was a good idea for EFI to read the partition table whatsoever should be fired).
The issue with PC hardware is, as it ever was, hardware vendors not following the standard. Much like Apple and OS X, they build some implementation and only fix bugs if they break Windows. So if you want to build a Linux implementation, you have to implement workarounds for all the quirks in different vendors' EFI implementations, and in the meantime you can't install on their hardware.
The issue with PC hardware is, as it ever was, hardware vendors not following the standard. Much like Apple and OS X, they build some implementation and only fix bugs if they break Windows. So if you want to build a Linux implementation, you have to implement workarounds for all the quirks in different vendors' EFI implementations, and in the meantime you can't install on their hardware.