My 3 year old MBP has one. Never been used. All it does is catch dust.
Ok. That's you.
WiFi is not the bottleneck, so why would I tie myself to a wire?
Wifi isn't always available. I typically configure wifi access points and other network gear using wired connections; because wired is working long before wireless is even turned on and configured.
I've been in hotel rooms that don't have wifi, but have wired as recently as last year.
I've been in client sites that don't have wifi but have wired as recently as this year.
Other times its absolutely the bottleneck:
I've needed to transfer 10s of GB of data between client and server in both home and office environments and waiting 20x as long for wifi to do it would be ridiculous.
I've used my laptop on occasion as an impromptu ISO storage to get citrix xen virtual machines installed ... glad i had gigabit for that too.
WiFi is not the bottleneck, so why would I tie myself to a wire?
If its available, and not a bottleneck, you wouldn't. But if you find you do need it... what then? You've got it. It added a nickel to the price of your laptop.
How can you be for Apple to make another nickel of profit (because its not like they pass that savings on to you)? What do you get in return for that? You get to carry an adapter around with you everywhere just in case. You get to shell out an absurd amount of money for said adapter. And murphy's law dictates that you probably won't have it with you when you need it anyway... wasting your time and money to source another one.