Are you talking about this video? There's a huge difference!
No case fans: CPU 71C, GPU 91C
1 case fan (exhaust): CPU 64C, GPU 85C
1 case fan (intake): CPU 67C, GPU 80C
2 case fans (intake + exhaust): CPU 60C, GPU 79C
3 case fans (2 intake + exhaust): CPU 58C, GPU 77C
4 case fans (2 intake + 2 exhaust): CPU 55C, GPU 76C
Airflow is very important, and an insufficient number of fans will definitely affect temperatures. Since small cases naturally have less space for fans, airflow becomes even more important for them. Given that a GTX 980 Ti is the hottest Maxwell card there is (tied with the Titan X, I guess), an mITX case is not ideal.
https://www.youtube.com/watch?v=YDCMMf-_ASE
Thinks he means this.