I suppose EFI systems don't have a way to pass parameters to the kernel, otherwise on newer systems there would seem to be less need for a separate bootloader at all. Presuming that EFI can't pass parameters (or an initrd) that seems like a missed opportunity for the Linux community to get native booting into the standard. Sometimes it seems like linux kernel developers don't participate in the right vendor clubs to influence the design of hardware and standards and end up needing to conform after the fact.
I'm just kind of talking out of my rear end here so maybe it's not like that at all but that's the sense that I get sometimes.
I wonder if grub EFI is an EFI loadable module or a more traditional x86 bootloader, something like that could have just been specified in the standard such that EFI could natively boot Win*, Linux, *BSD, etc. on common filesystems without any further installs or intermediaries. That would probably require compromise on the design which is always hard to get.