The truth is that it depends on your institution. My college required us to keep a somber tone, avoid dressing up how we presented things, etc. In other words, it had to sound incredibly boring. We were taught that academic papers were meant to deliver factual information. These other things didn't contribute to the facts or analysis, so they were unnecessary. I'm sure many other institutions might have variations of these rules. Break the rules, your paper doesn't make it. :(
Here's why I think that's ludicrous. ;) The purpose of any written work (excluding entertainment) is to convey a message. The writer must get the reader's attention, adequately get the message across, HOLD reader's attention while doing so, and (optionally) leave a lasting impression. Requirements 1, 3, and 4 are all in the presentation. So, it stands to reason that a witty, funny, or just somewhat unique presentation of content is entirely justified.
The irony of it is that many other classes taught us these principles of effective writing and captivating penmanship, then the academic papers we wrote were to avoid these things to be more successful. Makes a lot of sense, yeah?
Bonus thought. Academic papers also don't usually happen in a vacuum: many papers published in journals are competing with others. Different institutions want to make the best papers, find greatest discoveries, have highest acclaim, etc. It's not all that different from people publishing books. In light of this, I think academics have even more justification for going the extra mile to make their work stand out. Just a thought.