My guess is that either...

A) the cameras were not all set to the same "film speed" (in quotes because well, the D70 has no film...???)

or,

B) they're using different "intelligence" to meter the scene (as somebody already suggested).

What happens if you point both meters at something really boring like, evenly lit blacktop or a patch of grass (again, evely lit - either all in sun or all in shade)? The readings should be pretty close - especially if the cameras are both set to the same film speed.

Once again, you can do a sanity check by comparing the readings to the "Sunny-16" rule...