It's a common practice nowadays for one manufacture to produce the same component from multiple manufactures. Take Novarossi for an example, they are the ones that manufacture engines for Picco, RB, and some others. Now, all of the engines coming out of Novarossi’s plant are not equal. Each company has their own design and specification on how they want their engines built. It's just more cost effective for them to have the people with all the good manufacturing equipment "Novarossi" to make the engines for them.

Same goes for electronics. Each company "Hitec, Futaba, JR" will have there own specs for each servo, and even specs for the components used in those servos. It all boils down to money. Not every resistor that comes off the line will be exactly the same resistance that it's labeled for. But depending on how much that company wants there resistors to be the same will pay more for them, and other companies don't care as much and just take the slop.