Just my two cents on this matter.
But, the beastie bowling Jango over in the arena was DEFINATELY intended as an explaination for Boba's dent. There was no need for the detail to be so developed in that shot otherwise.
As many others have stated, the EU stuff does get trumped by any film stuff... hence many other explainations.
And, as far as screen accurate details go... Anakin's lightsaber in EpIII does not look exactly like the one passed on to Luke in EpIV.. nor does the SAME lightsaber look exactly like the one in EpV.
So Jango's Helmet is made to look just like Boba's because it's the same helmet. The screen details might not be exact from EpII to EpV (discounting the SE version) but George's intention is pretty clear.