I saw ntaw's post and my mind jumped immediately to Iniquity's example. Heh.
No, I believe you get one bonus attack for having 2 ccws. Walkers, on the other had, certainly do get a bonus attack for each additional ccw (Dreadnoughts, defilers, etc).
That said, if the walker comes with a pair of CCWs already (Maulerfiend, Soul Grinder), I'm told that they no longer get that bonus--it's already included in their profile, supposedly. Which does NOT apply to infantry--guh, confusing cluster-cuss.
What sphinx of plascrete and adamantium bashed open their skulls and ate up their brains and imagination? Imperator! Imperator!