There is always a trade off, in this case adding a second port would clearly complicate the design beyond design for a single port. Exactly how big a trade off that is I can't know.

As we've said, they made a very similar decision with the original Air and other machines before that.

Think about the iPhones and iPads for a moment. People said they were mad to not include removal batteries, SD cards and USB host support. People said they "must" add them in future versions. They seem to be doing fairly well despite resisting the urge to add them.

There were people who wanted those features, but they gambled on the fact that the majority of people didn't need them and that over time less and less people would need them. I think they were right.

They may well have stuck to one port on principle, the principle of aiming for where their customers are heading, rather than where the majority of them at at the moment. They've done that plenty of times in the past.