I'm not meaning to dis' 29ers, I'm just saying the bike industry tends to grab a particular segment each year and pump it up for application they were not meant for. Ubiquitous carbon and fixed gear bikes also come to mind on this front.

I would say for fire roads, I think a more traditional touring bike with 32MM or larger tires would be fine. 700c wheels give you a lot more options right now than 29ers, so I guess I'm saying that I don't understand the need. I could be wrong. This appears to be an experiment in the market so we'll see where it goes.