When they hadn't been released the game, Info on the MUA site said the you could modify the teams,...,..., and vehicles. Anyone knows why that has been removed.
....because it wasn't the case?
Maybe at some point they had it in mind that you could put your custom team logo on a quinjet, or choose to use either a quinjet, fantasticar or Blackbird to travel between acts, but it never got implemented.
Or maybe each character was going to get a car you could pimp and customize like in NFS?
The point is, it's not entirely unknown for not all ideas to make to to the released version of a game, and sometimes references to these scrapped ideas accidentally get left in publicity/adverts/interviews/websites despite not being in the game. I would guess thats what happened here.
Unless you can pimp your bumper-car.
BTW have you ever tried leaving three characters in the bumper cars then running off to anothre part of the level? They follow you IN the bumper cars sometimes, which is sort of kewl...