I tell you why I do John. When I was learning Hebrew from a Jewish person in Jerusalem, she asked me a very good question. She asked that if you believe that Jesus is the son of G-d, then why do Americans put his name on billboards and bumbers? And she had a good point. In Judaism, they are taught not to take the name of G-d in vain, and I think that that is a valid point. So I will not show my ignorance or disrespect for G-d...We leave out the vowel because it will not spell the whole name of G-d, but you know whom we are talking about.