I have to disagree with your comments on Ethernet: - there is security at the Ethernet level with 802.1x. Mostly used in professional settings, to prevent anyo

I have to disagree with your comments on Ethernet: - there is security at the Ethernet level with 802.1x. Mostly used in professional settings, to prevent anyone with access to an area to plug into an Ethernet jack and sniff traffic with ARP poisoning or access anything; - the ACK support for WiFi is perfectly fine at L2. The reason Ethernet doesn't do ACK is that the PER is very low so there's really no need for it. The reason why all wireless standards do some form of ACK is that wireless is very lossy and relying on higher layers for retransmission would give poor performance (retransmission at L2 is faster, and transparent to TCP). There's ACK for WiFi but in wireless LAN (e.g.: 4G/LTE) that are also lossy and with a relatively high latency you even have two levels of ACK: at the L1/L2 with HARQ, and at L2 with ARQ. Different contexts, different mechanisms.