I’ve shared John Gruber’s theory on this for a while:
I’m not sure why Apple hasn’t offered [4G networking on MacBooks] as an option yet, but my guess is that it’s because Mac OS X isn’t designed to behave differently while on different types of networks. With cellular networking, for example, you wouldn’t want iTunes to download new episodes of TV episodes or even podcasts in the background — a single episode could eat up your entirely monthly bandwidth allotment.
It’s been long enough since cellular modems in PC laptops became commonplace, and the MacBook line is diverse enough, that the omission of cellular options looks like a deliberate choice now rather than a “haven’t gotten around to it yet” feature.
When I first started using cellular modems, the only option was a $60/month plan with a 5 GB/month limit that ran at about 1 Mbps on Verizon’s new-at-the-time EV-DO network. Hardly anyone ever hit that limit — it would have taken about 11 hours of fully saturating the real-world bandwidth to burn through that, and in practice, it was hard to sustain those speeds for long. It wasn’t the kind of thing you’d accidentally do, and back then in 2005, people’s computers didn’t routinely download 5 GB of data unbeknownst to them.
With LTE, you can burn through a 5 GB data cap in an hour if you’re downloading big video files, and it would be easy to burn through the cap in just a few days if you’re streaming HD video — which, in 2013, is commonplace. And most people’s data plans have far less than 5 GB/month today. (At least they’re cheaper.)
I was hoping Mountain Lion would add some APIs suggesting cellular data considerations, but it didn’t happen. Maybe 10.9 will.
To start, Apple could just put cellular-connection detection and responsible-usage logic into iTunes and Software Update. That would be sufficient to launch with new 4G MacBook models at WWDC, then they could have a session on the new API and start enforcing responsible practices in the Mac App Store. Along with maybe working something out with Netflix, they’ll have addressed the biggest accidental bandwidth hogs that most people will face.
If Apple wants to offer 4G in MacBooks, they can start whenever they want. Doing it properly will just take a bit more effort than adding a modem.