I'm not a linguist, but I believe that it shares this characteristic with all older IE languages. In general, they evolved stylistic conventions that became set as rules. For instance in most Western European EI languages the convention was verb-second in declarative sentences, with the element one wished to stress first. This lead to subject-verb order as the norm in the descendents of these languages. (In interogative sentences it was verb first. Did you get that?) As English lost its inflections, it came to depend on word order to convey meaning. It shares this trait with Chinese. In spoken English we also depend on stress and tone to convey meaning.