Since Top Gear has been known to help the sales of cars costing from 10.000 pounds and upwards, there's no reason to believe it won't have an impact on a 60£ game at all.
Grimes; does it matter? Regardless of whether you have BBC or not, 350 million viewers get the same content no matter where and how they watch it. I know for a fact that 350 million do not watch it on BBC though, me and my pals have to torrent the episodes as they come in, I still watch it and I still love it to bits though!
Edit; nevermind, the show is huge and broadcast all over the world, we do see it on the state channel here as well, only it takes a couple of months before they air it.
http://www.autotrader.co.uk/EDITORIAL/CARS/FEATURES/33581.html
Edit 2; You can also read around for all the topics on car manufacturers and their relationship to Top Gear, these chaps really have a whole lot of influence and media power and a lot of manufacturers take it personally if this one programme doesn't approve of their car, and have been known to send them new and tweaked ones if they weren't satisfied the first time around. This speaks volumes of the kind of impact and credibility they have worldwide so we shouldn't be so quick to disarm the whole argument that this might boost sales somewhat, especially in Europe, who are absoltely bonkers about both Top Gear and Gran Turismo. To blindly state that this won't do anything for sure is rather silly imo.