The best reason I can come up for why retail and commerce has shifted away from the downtown, is that it is like many other cities in america. The car did it in. In the 70's leaders thought a facelift would help. So Main St was closed for a long period of time. This killed remaining businesses. To make matters worse, doctors and lawyers moved away for similar reasons (also fueled by our new adversion to downtown crime and percieved lack of parking (ha). Now banking regional/county offices and the left over textile industry corp offices, too. What is left is some lawyers, government, churches, and bums.
There is also an issue of who has and does own the buildings and lots downtown. One large player is an equivilant to aslum lord and will not cater or sell for renovation/refurbishing prodjects. He has also let his properties decay. Some more reasons for the lack of return to downtown is the recent downturn of it's economy and general lag in design and planning (due to it's misled conservative ideals of small gov. and bad taste alike).
As to the malls... Gaston Mall--the old one-- is on Cox Rd. It is the one in valley/depression (both economically and physically). The "new mall" was built in the 70's and has been renovated. I think Westgate(?) now owns it. It was "East(something) Mall." It has JC Penny, Sears, Belk, and Dillards as anchors. Maybe this has changed--I haven't been there in atleast 3 years.