Wood isn't necessary, I mean the action all happens on the pitch and if the opposition score then they could just cut to Lee saying "Ohhh, and xxxx have just scored!".
With Cho, the rumour I've heard is that a Korean singer has been asked; and not everyone in HP is a British national...Madam Hooch wasn't, and one of the Gringotts goblins was played by the guy who plays Mini-Me (Verne Troyer or something?).
Susan Bones wasn't English either.