when a user installs an application like Photoshop, he doesn't expect it to change anything outside of the operating system partition
This still does not make it right for GRUB et al. to call claim to that area of the hard disk. If anyone can write to it, for what ever their needs may be, then forethought should have said, "hey, this can potentially screw some stuff up. We should find a BETTER way". I use GRUB as my primary bootloader and I still cannot get on their side in this debate.
While that would indeed work, I'm sure there must be a better way.
One that always works is to put all the grub stuff into its own primary partition and make that one bootable.
Of course that would greatly complicate the installation process, but maybe grub can reuse some of the work that was done for parted.
If grub was in its own partition, the likelihood of it being broken by third party software is much lower. What could happen is that some software resets the boot partition flag, but that's easily restored.
In case of EFI, if I understand correctly, you can even mark any file on any partition bootable (blessing the file is the term, I think), which makes it even easier.
This still does not make it right for GRUB et al. to call claim to that area of the hard disk. If anyone can write to it, for what ever their needs may be, then forethought should have said, "hey, this can potentially screw some stuff up. We should find a BETTER way". I use GRUB as my primary bootloader and I still cannot get on their side in this debate.