So they can sell a lower price i5, as u can see the price of their unlocked 4670k and other k cpus they never drop in price and to sell a cheaper cpu they just sell it with a lower frequency. Being that the only cpus that can overclock far are the K cpus the rest i think can only go to the turbo freq but a non overclocker wont care and thus making the non K cpus ranging from the 4670 and 4430 for clock speed and then there other low power cpus or ones without a igpu and usually the difference is either the clock speed or the letter branding it has like the "k", "s" and "p" and that determines rlly what they will sell it at.
They put lower clock speeds on their cpus because they know that their single core performance is good enough to run at a freq like 3.0ghz. When u think of it the unlocked 4670k only runs 400mhz faster than that and OC it to the turb of 3.2 would prob be fine for gaming and even 3.0ghz.
Simply yes the 4430 is good enough and if saving roughly $40 matters then its a good buy