the triumph is one of those weird phones where clearly a few manufacturers used an older design and some clever branding to produce what sounds "high end" on paper for a low cost.
LG however makes some unique phones with generally good quality, even if the specs arent always high end. I think the Black will be a better OVERALL phone. little details will be improved on. its not so square, more comfortable to hold. the little things that make the phone easier to use day to day will be improved on and it will be more popular.
They already had a hit with the Optimus One line of phones, I'm sure they want to please that user base who are already going to look at another phone with the name "optimus"
also, the name "Optimus Black, is cool as heck!! haha,