I guess our definitions differ on what 'great airflow' in a case is. I used to own an Antec 900 and Antec 1200 prior to the Obsidian. While the airflow isnt bad, its not an Anty 900/1200 where you would see less of a change in case and CPU temps vs mine. It literally has one 140mm intake... not optimal with all that exhaust.
See the conclusion paragraph in my review:
http://www.overclockers.com/corsair-obsidian-800d-case-review/
Hell, just installing the 470 from GTX 260 216 and GTX 285, the case temps went up about 2-3C compared to both setups (which exhausted out side the case for ALL cards). My CPU temps went up about the same as well. So going from Anty 1200 to Obsidian was 2C temp difference, and then adding the card was another 2C on top of that for my CPU and thats WITH GPUs that exhaust outside the case. If I get all that heatdump inside my case, I assure you my temps will go up even more on other components. While that may not be troublesome to you, I benchmark and every degree C my CPU or system is cooler, usually translates to higher or more stable overclocks. So it matters to a lot of enthusiasts.
Again, its my personal opinion that I wouldnt want 200W of heat dump inside my case as regardless with any case really, all temps will go up. To deny that fact is just, well, Sillyness (sorry, its just that obvious to me). I'm sure it will be a bit different with only one gpu but maybe a 465 x2 will be coming like Galaxy promises.
While Im sure they are good coolers (I had one on my old X1950pro AGP IIRC), its not optimal to have so much heat dumped inside a case. You will undoubtedly affect other temps. Undoubtedly. And while you are right this wont be harmful to most system, every C counts for some, like me.
Im cooling the 470 with water and another radiator come this weekend anyway..
But I digress. Thats not what this thread is about really. So lets just agree to disagree and move forward.
Its peculiar that your experience differs from the majority and frankly goes against the laws of thermodynamics....