Getting a radio to communicate reliably with a computer proves to be a difficult task for some people. The trouble seems to be caused by USB to serial adapters that corrupt the data when used with certain software or at certain speeds. Whenever these problems are discussed in amateur forums inevitably the question of why radio manufacturers don't build USB interfaces into their radios (as Icom and Kenwood have started to do) is raised. I think this is a very short sighted view that really does nothing to solve the problem.
To begin, let's deal with the argument that goes "why force users to buy a serial to USB adapter when serial ports have been obsolete for years." Users have to use something to connect the radio to the computer and the only physical difference between a serial to USB adapter and a serial cable is that one end of the former is a bit fatter to accommodate the USB electronics. There is little difference in cost between the two cables. Furthermore, just because PCs don't come with serial ports doesn't mean that they are obsolete. My shack PC has four - soon hopefully to be increased to six if I can get it to accept the two port board I removed when I upgraded to four as an addition - and installing them is easily within the capabilities of any radio amateur. If you use a laptop you don't have that choice, true enough, but why force a change on everybody because some people choose shack PCs that have limited expandability?
But the main reason why I think building USB into the radio isn't the solution is that it doesn't address the problem. It's USB - either the hardware or its drivers - that is causing the connectivity problems in the first place. If an external adapter cable is used, users can try a different type if the one they have is not working correctly. If the USB hardware is built into the radio then they are stuck with it and reliant on finding a software solution. That might be a matter of getting the manufacturer to fix its drivers, which is not so easy.
Another reason why building USB into the radio is a bad idea is that it limits choices for users. If you want to connect your radio anything other than a PC, something like a MicroHam controller or a remote control over internet device for example, then you're stuffed if you've got a USB port. Some owners of Kenwood's new TH-D72 APRS handheld have already found that Kenwood's decision to provide a USB rather than a serial interface to the radio's internal TNC means they can't use Bluetooth to link it to APRS software on another mobile device.
Whenever I argue that switching to USB is a bad thing someone always counters the argument by saying USB can provide a wide bandwidth connection that can handle other things such as audio. As somebody who has sometimes had three USB sound devices attached to my PC I can certainly see how a one cable interface between rig and computer might seem attractive, especially to those who believe that sound card modes need something like a RigBlaster. And I would agree that a fast interface would be a nice thing to have if it was one that was a true universal standard like, say, Ethernet.
But if we are talking about USB, most of my arguments still apply. Built-in USB limits choices. An analogue audio input and output lets you interface audio with other things such as digital voice recorders, TNCs and VOIP devices for remote control over the internet. We're hams, we're supposed to be able to handle technical stuff, do we really need plug and play interfaces for our radios?
USB is a technology du jour. It keeps changing, whereas RS-232 and analogue audio are permanent standards. USB 1.0 devices seem still to work with USB 2.0 but now USB 3.0 is starting to appear and it remains to be seen how backwards compatible that will be with older USB devices. Who knows what the computers of 10 or 15 years time will be equipped with? It may not be USB anything but something completely different.
Finally there is the fact that USB depends on software to work: drivers that are operating system dependent. Most serial to USB hardware is at least supported by operating systems other than Windows "out of the box." I don't have the experience to know whether that is true for USB interfaces that carry audio or other information. Is anyone using their IC-7600 or TS-590 under Mac OS or Linux?
Even if the manufacturer-supplied drivers work for Windows today, will they work on the latest version of Windows in 10 or 15 years time? If not, will the manufacturer of the radio provide new drivers once the radio is an obsolete model? I'll bet a perfect but unusable as no longer supported scanner that they won't. I'm equally sure that I'll still be able to interface my K3's RS-232 serial port and analogue line input/output to whatever computing hardware and operating system I'm using then.