I asked explicitly what the differences are-- I also use the Speedplay pre-Pave cobblestone pedals so was curious about the new cleats. In a message I recieved in 2014 from Speedplay:
Thank you for contacting Speedplay.
There is a difference in cleats.
You can use a Pave cleat with Zero Pedals, but not Zero cleats with Pave pedals.
Any further questions please feel free to contact us again.
10151 Pacific Mesa Blvd. #107
San Diego, CA 92121