Depends in what kind of profession you are in. In the photo graphic editing and video editing area I am never be satisfied with only wifi, it just doesn't have enough speed I need to move files around servers. It is the mentality of Apple that doesn't gear their machines towards what professionals need in their line of work that bothers me.
Of course I will if I needed to. don't need to, I bought the non retina model. But this is the point why is something essential not already in a near 3000 euro laptop? Ok let's say they wanted to make it thinner and the ethernet is not part of that plan. But that's not it, it's all about selling accessoires to make you pay "again". They could have thrown that adapter in for free, but chose not to do so.
They could have followed the standards instead of creating their own ports and plugs, but they chose not to do so .. because they want you to spend even more money.
I joked about this for a while but I now I really wonder when Apple will drop the usb standard and create the same thing with a different plug and a fancy name to sell you more of their awesome stuff.