Bin Laden doesn't use the term "God". He says "Allah". If the interpreter said "God", it was an erroneous interpretation.
"Allah" IS Arabic for "God".
Anyone interpreting Arabic is completely proper to say "God" for "Arabic."
Which is one of the reasons "Allah is Great" rings so false in the Anthrax letters. If it truly was someone Arab writing in English it would either be Alluhu Akbar" or "God is Great" most likely, not mixed.