you dont get it, few tens of computers, or even hundreds are not going to influence total network hashing power NOWHERE near as gpu or asic farms, where gpu is worth several cpus alone, not to mention ridiculous disproportion when it comes to asic farms.
this allows general population not only to mine but also seriously contribute to network security, power in numbers and decentralization.
i'd say bitcoin is no longer as secure as it was during cpu mining period. because most of hashing power is getting centralized firmly in the hands of several asic mining cartels, who can manipulate both price and security.