Remember when Apple first started killing off "legacy" ports and such (floppies, ADB, SCSI, serial, etc.)? Now we're clearly seeing the downstream effects of that sort of thinking. A buddy of mine has a very expensive film scanner with a SCSI interface. The scanner still works great, but he has to keep around an ancient computer to run it. (Yes, there are USB-SCSI adapters, but then you have to worry about whether or not you've got the right one, much like you're worrying about specific USB-Serial interfaces. And as film itself is going away, the need for that scanner will also eventually go away.)

Kinda leads to an interesting question of whether USB has "won" or whether it, too, will one day become a legacy interface. I'm kinda thinking that USB may truly become the one true interface, although future USB might well be quite different from what we call USB today. USB 3.1, for example, has a connector not unlike Apple's Lightning. I'm similarly amused at how USB is increasingly the default charging interface for all sorts of otherwise-dumb rechargeable devices (e.g., the headlight and taillight on my bike).