They all require a host driver of some description, in the windoze world they are called VCP or virtual comm port drivers because they make USB look like a serial port on the host side. Your micro based app sends stuff through the serial port, and your host SW uses a standard serial driver provided by the chip manufacturer. It works a treat except for really high speed apps just as pmoyle suggests. These types of devices are available from TI, SilLabs, Cypress, FTDI, Microchip and probably quite a few more that I haven't read about yet.
I've been using the CP21xx devices for precisely the purpose mentioned for more than 4 yr now. The one glaring omission from his article is the bandwidth discussion. If you need to transfer lots of data fast you need full blown USB. My requirements for instrumentation and test interfaces are fairly minimalist and the scheme works well for that. Also on low volume/one off projects the effort required for full USB is over the top.
Let us understand that this article is being written by a marketing engineer. That being the case, I think he has put his thoughts out well. At the least, I understand that I can use such a serial to USB solution in my designs without having to go through the learning curve of USB interface specification understanding (at least not a thorough understanding).