Well, most people have other gadgets. You know, GPSes, Radar Detectors, Jamboxes, and such. Sometimes they need their firmware updated. And you need a USB connection to do that.
Sometimes you get a CD or DVD, and you need an external drive to read it. Not all media comes from iTunes.
I'm not sure how much better a laptop can run Quicken than a Surface Pro. I mean, its just Quicken. The fact that it RUNS is what's important. That and the multitude of other software that doesn't like OS X or iOS, being that they only run on less than 20% of all devices, the other 80% mostly being Windows. So running a full version of Windows with external connectors is, well, MY definition of functional.