The metallurgy that goes into making rotors has to be amazing. I liken them to samurai blades because the red hot steel is cross-folded and flattened repeatedly... like in swords or cymbals where the molecular direction of the material becomes cross-hatched. Sometimes my rotor develops a slight side wobble from a knock, and this slight bend disappears after a really hard brake run. It gets really hot and when it cools down it kinda self-straightens because of it's metallurgy... I can't remember the correct term for it.
The cut-out patterns are not only there for cooling, and dispersing trapped dirt, but also for controlled expansion. Remember that unlike motorbike and automotive counterparts, bicycle rotors are only 2mm thick!
On extended downhill braking sections, these rotors get so hot you'd get heat-branded if you touched them. The outer "ring" expands more than we realize and the funny shapes are there also to control expansion and contraction to minimize metal stress and fatigue.
That's one of the reasons why the "spokes" on the rotors are usually curved and not straight - and why rotor designers prefer narrow pad contact areas rather than wide ones like in cars and motorbikes. You also have to take note of the "arrow" for the direction of rotation when installing them. The shape is deliberately stress oriented and it would be detrimental for the rotor if installed the wrong way.
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