The stepping is a revision within the same cpu type. You are right that it is a version change. When a line of CPU's with a particular stepping reaches its limit (such as the cA2 stepping topping out at 800 MHz), intel will create a new stepping to reach a higher level. Thus, cB0 went to 1 GHz, and cD0 is supposed to go 1.13 GHz (cC0 was the famous failed attempt to reach 1.13 GHz).
The great benefit is that intel does not run parallel production lines, so once a new stepping is introduced, then entire current production line will be made with that stepping. As long as there is demand and profitability for a certain processor, intel will keep making it. Therefore, new steppings can be great for overclocking, because when low speed chips are made with steppings intended for much higher speeds, there is much more room for overclocking. Consider a PIII 700e made with cC0 stepping, which was intended to run over 1 GHz--most people are getting them to 933 or 1 GHz with little effort.
However, there is a contrary theory popping up that new steppings can also be used to resuscitate low speed chips that would otherwise not make the QA grade and would be destroyed.
Hope that helps.
