Yes, DTM is is not a modified car, most other serieses require the body shell to be intact (DTM keeps only the roof afaik).
The problem I have with most tc serieses is that the badge is just a badge, I can't make a decision to buy a Holden or a Ford based on who wins Bathurst (except to buy whatever Lowndes is driving)
I would like to see a showroom stock series where cars were classified on purchase price. Real consumer advice. Minimal modifications, apart from the obvious roll cage, seat and belts.
Allowed to remove: cockpit trim, to compensate for the added weight of the roll cage (and limit fire hazard). Replace break pads, maybe shocks and springs. Safer gas tank. Require large series of production, and car to be available for purchase (to limit cheating with the price)
Make the races classed on Euro NCAP stars too so I be tempted to buy the fastest safe car instead of the fastest cheap car.