I agree, killstreaks and scorestreaks are effectively similar but with the added bonus that every action you perform that grants you score advances your streak. It's a new form of awarding players for team based activities and objectives.
It isn't "new" at all. Please quit parroting the Treyarch party line. MW3 had "killstreaks", but taking out a UAV or enemy equipment, or taking a flag in Dom added to the streak. So the scorestreak isn't anything new or fresh. In fact, it's EXACTLY what's been done before. Just with a new name.
Actually, now UAV's and other team assists add to your score streak as well. That is what I'm referring to that has been newly introduced.