Actually Boba was supposed to have a neck sealer. Look at the Star Wars Chronicles book. They made an attachment that velcroed along the front half of the helmet (under the chin) and then velcroed to the neck of the quilted balaclava they used on the pre-pro suits. They didn't use the neck sealer in the films, but continued to use the quilted balaclava.
Since Jango doesn't have a high neck seal around his throat and just a collar with a balaclava, yeah I do kinda find it silly looking when I see Jango costumers at conventions with visible necks showing from all sides since they don't wear the balaclavas.