The lack of wired Ethernet is one of many factors that makes this a "road warrior" laptop and not the "desktop replacement" that nearly all Apple laptops have been for the last 15 years. The slower processor and limited storage capacity are also biggies.
Apple has tended not to offer dock accessories, since the days of the Duo, leaving that space as a third-party add-on opportunity. I'm sure the BookEndz folks are contemplating an adapter that plugs into the headphone jack, USB port, and micro-DVI port on the side of the MacBook Air, but most users will probably never bother. This thing's screen and keyboard are good enough that the average user will never need to hook into desktop-based equivalents, which is the main reason people use docks.
It's worth noting that most laptop users EVEN NOW aren't bothering to plug into wired Ethernet, even when they HAVE the requisite port on their laptops. I strongly suspect we've already seen a large chunk of the hit on Red Rover's capacity from the shift to wireless, and Apple is just giving in to reality by leaving out a port no one is using.
The folks who want wired Ethernet can buy the inexpensive USB adapter Apple is offering, and we can certainly suggest it. That'll especially come in handy in areas of campus where Red Rover isn't yet ubiquitous, but in areas where it is, I don't think anything changes... I think wireless use is going to continue to ramp up whether the manufacturer provides the wired connector or not, especially since Red Rover is already sharply faster than the switched 10 Mbit wired pipe we've still got to so many desks. We just have to keep up with capacity demand.