Figure I will throw my 3 cents in being a convert from off-road to on-road 200mm touring.
The whole thing is can be boiled down to a few things:
1. Access. I switched because there is now an on-road permanent track within 30 miles of my home. I like on-road because it's closer to "real racing" to me. But if 301 did not exist, I would still be running my T-Maxx and Revo.
2. Commitment. It takes a lot to switch because the off-road scene is easier. Not a knock to the off-roader but getting as Revo/T-Maxx ready to race is a lot less intense (time and money) them getting a MTX-4R or NT-1 ready for the track.
3. Such a big difference between the RTR and kits in 200mm. For the most part, you can buy a Losi 8ight RTR and with not effort, make it a pro-level racer. There is no current 200mm RTR that can realistically be made competitive against the top cars (with the exception of may be the Team Magic car).
4. Coverage. Most major magazines cover off-road in more depth then on-road. Also, I will say this to I am blue in the face, if ESPN can show poker 2 hours a day, every day, there has to be time for/interest in R/C racing.
OK, rant over.