You must be talking about public hoppers in Forza 3, the private lobbies (that you set up with your mates) from day 1 has had a gazillion options/restrictions, you can set all assists on/off individually, you can set whether 'tuning' is allowed, whether damage is cosmetic/limited/simulation, class of cars, types of cars, PI limits (low and high), you name it, it's pretty much there.. Even staggered starts/ and can even set that fastest lap wins.. All it's missing is some of the organised racing niceties like automatic qualifying etc. GT5 is just very rudimentary at the moment.
You also have to consider that assists are different in FM, generally you can go faster/brake hard etc with no assists on, it's only very high power RWD cars that benefit from TCS.