Why would a machine have a heart?
Thats one thing I never understood in Terminator Salvation.
What's to understand, they're infiltration units. Why would a machine need real skin, blood and sweat. The idea is to sneak them into the resistance without being discovered, Marcus was the latest evolution of design, intergrate a real brain and a real heart, now you have a programmed machine that has memories, personality and a beating heart, things that people can perceive without cutting you open. Blair had no idea he was a machine because of it and it was perfect for his mission, had he been clearly a machine, Reese would have taken him out before h ever got near Connor.