Yes, I actually reflected on Muay Thai roundhouses employing similar diagonal kicks. Is the only difference the point of foot making impact? If thats the case, WTF roundhouses are actuallythe same as in MT! Funnily enough.
I stress that not all MT kicks are like that. Like the post on Sherdog mentioned, any MT instructor worth his salt will tell you to turn your hips over for more power. Also, any good instructor will explain that a ball of the foot round is different and is used differently depending on the effect you want to create.
You will find that martial arts styles draw on a very long and similar heritage. The more you look into it, the more similarities you will see.