I think you will find that a lot of programs... especially the better programs require some sort of "hoop" for you to jump through to apply to them. That could mean a non-standard LOR, a special additional letter stating why you want to go there, a specifically formated PS, or some other transcript, like MCATs or Undergrad transcripts.... The point is, it really doesn't matter what extra hoop they give you, the point is to make you do something more to apply to their program than simply "check a box." Many programs simply put these requirements in as a way of acertaining whether you are willing to go the extra mile to apply to their program.
And make no mistake... this "jumping through extra hoops if you want it bad enough" will continue throughout your career.
Best of luck... it's a challenging time