Since when was the grave accent character a modifier or dead key on a computer keyboard? Using a compose key is one thing, but colons, carets, and tildes aren't magically combining with letters to form letters with diaereses, circumflexes, or tildes above them.
On many non-English layouts there are dead keys, and the ` key may not exist, except as a dead key.
For example, the letters å, ø and æ are very common in Danish, so they have their own keys. The acute accent is sometimes used to mark stress, like é or ǿ, and this is done using a dead key -- it wouldn't make sense to have several keys just for this purpose.
