I was looking at the benchmark tests for the nexus 5 phones, and even intensive tasks like 3d gaming use 2 cores max. Even basic multitasking tasks like streaming music while surfing the web wouldn't need that many cores either.
Even for laptops, Apple still ships their MacBook Air laptops with dual-core processors, and they are no less capable for the majority of tasks their customers use them for anyways. The stuff which may need more cores, like video editing, aren't stuff you would typically do on your phone anyways.
Since we are in the topic of cores, can anyone tell me what you do on your android phones that actually make use of all 4 cores?