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.

Windows does this with the US International keyboard enabled. `+a=à, '+e=é, "+o=ö, etc.

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.

http://fontmeme.com/images/danish-keyboard-550x183.png