This is another intellectually dishonest metric to use for performance comparisons. It has also been discussed to death in other threads, but I'll attempt to summarize.
First and foremost, 60fps is a design choice, nothing more. You can choose between a crazy amount of effects, or tone them down (compromises are the key to developing on a closed box system) and reach a higher frame rate and resolution. This is why you see effect heavy games like Ryse at 1600x900 on the same system as a 1080p Forza.
Driveclub and Forza are doing completely different things. Driveclub uses dynamic lighting, whereas Forza primarily uses pre-baked lighting. This is part of why there's no real change in time of day for Forza, whereas Driveclub has a day-night cycle. So the lighting and shader technologies in each are totally different, with Driveclub as the arguably more advanced, "next-gen" approach. Because of the differences in what they're doing from a technical standpoint, Driveclub uses more of the system's power on things that Forza isn't even attempting. This leads to Forza being able to render more frames per second, because there is far less computation having to be put in each frame.
I'm not very technically inclined, so I used some caveman terms in that summary. If there's any GAFers that are more proficient, I'd welcome a better-explained version of what I just said
EDIT: Further clarification of my argument. There are also more realistic reflections in DC. The result of the pre-baked lighting in Forza leads to the shadows of trees and buildings looking "pasted on" the pavement, and though the sun appears to shift slightly in that one video, the shadows are not affected by this change. This is because the shadows outside the cockpit are not dynamic.