THe bag of treats you saw were probably just regular treats with a cutsy name. Not actually marrow bones. Those aren't usually sold in bags like I think you're talking about.i saw a bag of treats called 'marrow bones'. or are you talking about the real marrow in bones? i give my puppy chicken quarter, do they have marrow bones on there??
And yes, all bones have marrow in them (I'm pretty sure, at least). But the bones being discussed here are weight baring bones from large animals. Many people just refer to them as marrow bones or soup bones.