Academic writing does indeed differ from other types of writing. Let me list three ways in which academic writing differs.
First, academic writing is formal in style. Personal writing does not have to be formal and often times it is not.
Second, academic writing is based on extensive research and seeks to prove a point within an academic field. This alone makes it very different than any other type of writing. For example, in academic writing you have to back up pretty much any statement that you make with extensive footnotes or original research or field work, and you need to show that you know the history of the scholarship very well.
Third, academic writing is meant for a specific audience. It is not for the general public. You are writing for your academic peers. So, it will usually be highly technical.