Gamespot quote is about the cars only, which might be right. But that is not what the IGN quote is about.
Have we seen any 'autovista' style car porn in driveclub yet, or only from the races? Aren't the forza 5 cars much higher detailed in the garage than in races?
I don't think it is unreasonable to compare them, as they are both big first party titles and both racing games. Context should be taken into account though, bearing in mind the different styles (sim/arcade) and graphics focus (30 vs 60 FPS)