Not to rain on the parade, but by mods, I'm not so sure they mean car mods, as in adding cars, but smaller modifications to alter the game experience. I believe adding cars would take a it step too far, and possibly even allow people to cheat by altering the stats of cars, which is precisely why the release of cars was controlled by Atari when the online portion of the game is such an integral part of the game.
I wouldn't want to be the one caught doing something due to a mistranslation issue. I would much less like to be the one caught with my pants down. This could be disastrous to the community.
So, to clarify, I think what this announcement is saying is they're OK with sound mods, wheel rim mods, colour mods and night-time/fog mode. The minute that people start bringing in new cars that Atari hasn't officially OK'd, that change the game's impact for others, I think that's when problems will arise. It won't matter if they're the same models as on the X-Box, but that introducing them onto the PC version without Atari's consent will cause them to raise a red flag. That's not something the community wants to happen, does it?