They were special cars introduced in Gran turismo 4. They are not able to be raced anywhere except in the practice runs or in Speed tests. Maybe thats why they took them out.
I'm not too sure if the 2022 or the MTRC are even in GT5. But the Caterham can be raced normally due to the PS3's increase in RAM compared to the PSP & PS2.
I'm pretty bummed that they took out these cars. I love oddities (yes, even the Benz Patent Wagen).