I think that's a good thing. You'll see it from time to time with other software as well. vB has a couple of IPB look alike styles and vise versa. PHPBB has a Simple Machines theme, there are probably tons of more I bet.
Whomever designed this made one vital mistake. They did not use a highlighting gradient which is just a simple gradient but it re-sides in all the categories (category-23px-light.png). This sets the visual apart and eliminates that flat look. Infact, I said to kier the way he implemented this was really quite genius as older browsers take note of this gradient. The copied theme doesn't even show that on new browsers but then he/she probably didn't notice.
The background/body is one colour therefore lacks that visual separation that makes the xenforo style one of the best (if not the best) default styles on any product.
My tip of the day. Notice the little things, they'll make the biggest impact if implemented correctly.
Very incorrect. And I would know considering I used to be staff there.
In regards to the topic at hand, the MyBB Community has a certain knack for creating styles based off other software, rather than taking a unique approach. At least they did a few years ago, I wouldn't know now seeing as I'm no longer active in their Customization community anymore.
Almost every theme that was made for MyBB was modeled after vB3. In fact, most them of them actually created a navbar exactly like the vB3 one. There were many times I had to inform people that using vBulletin Graphics was against the law, and I even had to report a few sites after they refused to take the images down.