Phone manufactures sell phones to carriers, not consumers. Success in the phone industry depends entirely how well you meet the demands of the carriers. RIM knows it (or knew it), Nokia knows it, Samsung knows it.
Android is merely a platform that allows Samsung to tailor their devices to the carrier's requirements, in a way they couldn't do when they were selling Windows Mobile devices.
So how does Android 4 help Samsung better meet the demands of the carriers?
It doesn't. Carriers want devices that show off their network, they want devices that compare well against the iPhone, and they want you to buy a new phone and sign a new contract in 2 years. They obviously have no trouble selling Samsung devices with outdated software to the unsuspecting public; it made Samsung the largest smartphone manufacturer in the world.
Neither the carriers nor the manufacturers will spend a dime to rush out Android 4.