Well, my information is a bit different. During his time, there were many amateur mathematicians around. And Newton had a long standing beef with Leibnitz (Who was the chair of the Royal Society at the time). Whenever Newton published any paper, these wayward mathematicians used to ridicule his ideas, which infuriated Newton. That's why he decided to write in such sophisticated and grandiloquent language, such that these dabblers won't understand what he has written, to teach them a lesson (Irony, ROFL!! :D)
Small corrections: while he did indeed have a rivalry with Leibnitz (over who invented Calculus), Leibnitz was German, and therefor not likely to be chair of the Royal Society. You are probably thinking of Hooke whom he also had a rivalry with.
