Chipsets are what makes thin laptops possible. Lower power requirements means less heat, less heat means tiny fans or no fans (depending on clocking etc), and less power requirements means tiny batteries, which means less weight.
My point is that Apple did not "invent" thin laptopts. Thin laptops are a result of advances in chipsets, namely Intel´s Atom, and now AMD´s Fusion "APU" (CPU+GPU all in one).
Apple is not a semiconductor company, it just has to use what others have to offer. It could be alleged that the rise in popularity of Apple´s computers were after OS X and the switch to x86 CPUs.
Old MacOS machines were quite dogs, not to mention the original monocheome Macs at the time when the Commodore Amiga had real multimedia, superb sound and color, on top of an OS with true multitasking.
Of course history revisionists would like new generations to believe the Amiga never existed, but it did, and it kicked Apple´s butt.
FC