Ethernet cables have saved me quite a few times while installing Linux. (But that's irrelevant to apple, they don't even need to concern themselves with drivers.) Besides that I haven't really needed an ethernet cord all that often for my laptop. (Or at all really.)
For my desktop, depending on your definition of "use" (If that means installing an ethernet cable, or connecting to a network with one.) I last used one a few weeks ago, or right now.
About the only time I physically connect some of my machines is for a network boot to install Linux.
It's not that wired ethernet is never required, just that wireless is perfectly acceptable for the vast majority of users.
As an aside, if an office is paranoid enough to lock down well encrypted Wifi, I wouldn't be surprised if Thunderbolt got the boot as well.
It's built like Firewire; devices that are plugged in have direct access to the host machine's memory. Though at least it now has the ability to mask off sections of memory.
An attack via a malicious network adapter doesn't sound out of the question. Seems like it would be on the same level of plausibility as sniffing WPA2 traffic and decrypting meaningful information from it.
Is there a likely hood of WPA2 AES being cracked? Yes, it is very small but it is still possible. Also if a secure device is captured by an attacker and they steal the credentials to access the wireless network they can now come and go as they please. At least with physical they would have to enter the building and plug in.
Are other attacks feasible, absolutely and I will grant that, but having wifi enabled just doesn't work for certain situations and where paranoia runs high due to the work that is being done.