Crytek would like to take the time and give you a global update on the multiplayer part of Crysis:
"As for the DX9 version we won't have physics and day and night cycle in-game. That means you won't be able to shoot down trees and/or alter any other objects than vehicles on the map. [...]
Rather than providing the community partially working features we limit this for the DX10 version only. Due to the strong hardware available with DX10, server load is less and performance is increased. [...]
Gamers with a DX10 card are able to play on DX9 servers, but with the limitation of the respective server. Vice versa it is not possible for gamers with DX9 cards to play on DX10 servers due to the limited features."