What am I missing?
Hyperthreading . Você tem 4 núcleos físicos, mas 8 lógicos.
For each processor core that is physically present, the operating system addresses two virtual (logical) cores and shares the workload between them when possible.
Veja também os dados da Intel no seu processador, o i7 4870HQ :
# of Cores 4
Cores is a hardware term that describes the number of independent central processing units in a single computing component (die or chip).
# of Threads 8
A Thread, or thread of execution, is a software term for the basic ordered sequence of instructions that can be passed through or processed by a single CPU core.