Why use Allah when you're talking about Muslims and God when you're talking about Jews or Christians?I could be mistaken and it could be different in English and German, but the main reason I see for that use is politeness. German Muslims get very upset if one uses the word 'Gott' when 'Allah' is meant. They see it as a kind of Western arrogance expressed in language and don't feel taken serious.
May be next time Tony Blair just addresses Bertie Ahern in a letter as 'prime minister'. Basically the same thing is meant and spelling errors are less likely than with 'Taoiseach'.
Wolfgang