The stereotypical view of professional academic writing is that it is grammatically complex, with elaborated structures, and with meaning relations expressed explicitly. In contrast, spoken registers, especially conversation, are believed to have the opposite characteristics. Our goal in the present paper is to challenge these stereotypes, based on results from large-scale corpus investigations. First, we argue that both conversation and professional academic writing are structurally complex, but their complexities are dramatically different: in some ways, conversation is more structurally elaborated than academic writing (e.g., finite dependent clauses are more common in conversation than in academic writing). In contrast, written academic discourse is actually much more 'compressed' than elaborated, with phrasal (non-clausal) modifiers embedded in noun phrases being the major type of structural complexity found in academic writing. Our historical analysis shows that academic writing has changed dramatically over the past century to prefer these compressed discourse styles. Second, we argue that a consideration of the meaning relations among structural elements illustrates that academic written texts are anything but explicit at the grammatical level. Rather, the 'compressed' discourse style of academic writing is much less explicit in meaning than alternative styles that employ elaborated structures. Again, our historical analysis shows that academic writing has changed dramatically over the past century to strongly prefer these less explicit styles of presentation.