Earlier quoted context omitted.
Well the MacBook Pro's are ultra portable and super thin now. The laptop would probably have to be at least 20% thicker to make for enough room for an ethernet port. And since 90% of MBP Retina owners probably rarely if ever use ethernet, it's a good tradeoff to make. The Retina model is much lighter and easier to carry (especially with one hand) than it's predecessor.
I think Apple could have come up with a solution without compromising on this. What about a neat folding Ethernet port that flips out and is flush when not in use? I remember some old ThinkPads had something like that but it might have been a modem port (RJ11/RJ14 not RJ45). The rare use is what makes it a problem. It's not worth the investment to buy and always carry an adaptor for that one time you really need it.
although adding the 3.5mm headphone jack to an auxiliary board was super smart. people keep dropping them with headphones inside.