FYI There is a new cable that Mitch released for the HD tuners. It is now USB so you dont have to deal with any USB to RS232 adapters. You can find the cable here
To answer your question -
Yes, the HD radios will play regular analog AM and FM, as well as HD broadcasts. Many stations have simultaneous analog and HD broadcasts, and the HD tuners switch between analog and HD depending on reception. HD broadcasts also can have multiple feeds accessible by HD tuners - essentially two stations on the same channel.
Also, take a look at Visteon HD tuners on eBay. I looked the other day to check prices in case I need a new one (2 years running on my current one). They have several at great prices, both new and used. Also, these units are built for a car environment and should take a pretty good beating.
I use Mitch's serial cable to a serial port and have no problems. You can always use a serial-to-USB adapter, which is essentially built into his new USB cables.
The radio works great in a variety of skins in Ride Runner. I am currently using DXF 5.03 and can tune all the local stations, both AM and FM with ease and get great reception when connected to my stock antenna with an antenna extension cable (the unit is mounted in the trunk).