Why 802.11use acknowledgements but not in wired Ethernet?
Two scenarios exist where
a wireless network might not know if a frame was successfully
delivered, that do not exist in a wired network. First, a weak
wireless signal could mean that the sender may not be capable of
transmitting and listening at the same time, and this makes
collision detection impossible. Second, fading or the
hidden-terminal problem could mean that interference occurred
during the transmission without the sender knowing.