Ah so you believe, like the others, that since Apple released their iPhone form factor, everyone else had to copy that.
This isnt about doing what your competitors are doing. Its about gaining sales.
I cannot think of a reason why a smartphone now would want to use a dual core processor or better yet want to POWER (power = batter) a dual core processor. Make no sense at all.
As of right now, I do not see any marketing from any company stating "This is a (company name) (model)! It has dual cores! More cores more..." whatever. What you have said is true but for now no company has used it as a excessive market sheme AFAIK
Motorola Atrix: Great phone except no keyboard, internal storage is low compared to the N900 (for example), and resolution is kind of strange (Android issue). LG Optimus X2: Nothing too special (compared to the Motrola Atrix) except the dual core. Low storage (compared to anything). This phone could be released exactly the same without the dual core and it wouldnt make a difference as it has been shown that a single core can also record 1080p.