It's just about the language of the title.
You could say will Britain ever produce a player as good as Federer, or Agassi, or Samprass because these guys didn't come from GB. Or you can say will britain ever again produce a player as good as Perry or Henman or Murray (although we don't know how good that'll have to be cause we don't know the full extent of his greatness) But you can't say will britain ever produce a player as good as Murray because we produced Murray! The question answers itself.
It's like saying will Liverpool ever have a captain as good as Gerrard. Of course they will, they have him!