It's all about braking control and tuning brake balance. Driving without abs is great in forza and works perfectly when you learn to use the controller trigger like a pedal.
No i have never tried slamming my brakes on at 150mph because my car has ABS, isn't stripped out to 900kg, isn't kitted out with some crazy 378mm ceramic disks, isn't pushing over 400hp, isn't using racing slicks, isn't using fully adjustable suspension and isn't using 300lbs of downforce. Then again you have driven all these "factory works" supertourers (which is what they basically represent when fully upgraded) in real life right? Braking at 150mph you just pump the brake pedal.....
Try something like the Saab 9-3 Aero. Drive it around stock. Can't fault it compared to the real thing.