It seems like you're confusing COMBINING GRAVE ACCENT and GRAVE ACCENT. These are two separate characters with distinct code points. One combines, the other does not. It's not a property of the font; it's a property of the characters.
Yes they are unique characters. I went to some pains to ensure I used the word 'key' as in physical switch on a keyboard. However I did not go far enough in ensuring I was referring to the font package as opposed to the font, please accept my apologies.
http://www.fileformat.info/info/unicode/char/0060/index.htm
http://www.fileformat.info/info/unicode/char/0300/index.htm