I agree it depends on the context it is used. Is it an idea or a place? saying that you live in a city but do not capitalize it is not the same thing. For a believer there ar many cities but only one Heaven, Also Biblically speaking, Newer versions of the Bible capitalize Heaven in certian circumstances ie: The Lord's Prayer....but in the King James it is not capitalized. The difference there has to do with modern English VS. Shakespearian English.