With Natural Selection, their beta 4 patches were merely to level the playing field between different alien classes and marine classes. There weren't any changes to gameplay. Things like changing the cost of points for different skills, changing health and armor statistics for different classes, and minor map tweaks are neccessary patches for NS. Their big releases take a long time to put out, so they don't want you playing their game with unbalanced classes-- this is the reason for their patches.
ESF doesn't have this problem because things are about as balanced as can be. NS has more aspects as far has armor ratings and skill point investing. If they don't keep things balanced, no one will play on the weaker classes-- which can result in bad team play. Imagine if no one picked the Gorge as a class because he had the worst dmg and his offensive chambers were easily destroyed-- there would be no res towers, defense/sens/movement chambers, and no class to heal structures. Such an unbalance would ruin NS.