You have to wonder if they knew the tracks would fail like they did and figured it would make good tv, or if they just didn't have a clue and found out along the way that they don't do potholes very well.
The tracks probably gave Hammond better gearing, which means his hot hatch did fine crawling over rocks. Once he switched to standard sized road tyres he had to abuse the clutch to crawl over stuff and that's where it failed. And that's why torque converters are superior.
It would be interesting to examine the AWD system after all that abuse, though. The Focus (like the current generation Opel/Vauxhall Insignia) doesn't have a rear diff, it just has a friction clutch for each rear wheel and a brain box that applies power individually as needed. GKN Twinster.