I don't claim to know everything about insuring these vehicles, but I spent a good two hours on the phone with multiple insurance companies yesterday and I wanted to share the information. Looking over the site, I think there are some individuals who may be carrying an incorrect policy and it could come back and bite them should they ever have to submit a claim.
USAA requires a commercial policy (through Progressive) when the vehicle is rated over 1 ton or 10,000lb GVWR. Texas law places the limitation at 25,000lbs. USAA has instated these restrictions to keep premiums as low as possible for private policy holders. The same holds true for State Farm. Anyone who has an Antique/Collector's policy through their insurance company must realize that (usually) the truck cannot be driven more than 1,000mi/year, be used to haul anything, be driven for recreational purposes (parades/shows only), or stored anywhere other than an enclosed and locked facility.
I asked Progressive why my vehicle was categorized for "Farm" use on my commercial policy - they are using this category as a catch-all. They used to turn away MV owners altogether. I spoke with a senior underwriter (from State Farm, not my insurer) and he assured me that my commercial policy was the only way I would be covered if I submitted a claim for an accident that occurred on the road, as long as my vehicle is street legal and I am not using it for business purposes.
There is another consideration when carrying a commercial policy - radius. Companies are charged premiums based on the range they travel. My policy is on a 50-mile radius, but I am allowed 4 trips/year outside of the radius. I can take the Deuce 1,000 miles away, four times a year, and be covered.
I hope this clears some things up. It sounds like some people may be carrying an antique policy for the cheap premiums, but please ensure you are within the usage limitations if you choose to do so.