DMVPN labs from v5 workbook - mGRE on the spoke routers?

Hi,

Since there is no v5 workbook subforum I will post here.

I started doing the new DMVPN labs and noticed that everywhere on the DMVPN spokes the tunnel is configured as mGRE.

I thought the mGRE on the spokes is needed only when implementing phase 2.

Is there any particular reason why the spokes aren't configured as p2p GRE tunnels?

Thanks