According to PSX Extreme:
"There are those in this industry that cry with anticipation for a new Halo. Others for a new Mario. I'm neither of those. My kryptonite has, and always will be, the most ambitious racing franchise in existence: Gran Turismo. For the past ten years now, Gran Turismo has been Sony's most successful franchise, in addition to being one of the most popular in the world. With only four games under its belt, the series has sold an astonishing 50 million copies to date. ..."