I'd argue Gran Turismo has a unique audience with a lot of people who normally don't play games and both 3 and 4 surpassed 10 million.Please post a list of best selling software on ps2 sold to casual audiences in comparison to shit like Wii sports
According to the list on Wikipedia (ego ignavus) Eyetoy sold 4 million, Guitar Hero 2 sold 3.4, Finding Nemo, Lego Star Wars and The Sims at 1.4. Single sales only so with Guitar Hero especially there are tons more sales combined.
It was scewed much more towards the male audience and didn't have as many individual mega sellers like we have today (basically just GTA and GT), but it also had a lot more smaller titles that are dead now like Tony Hawk, Jak & Daxter, Ratchet and Clank that all sold several million each. I wanted to include more of the casual titles directed mainly towards men like sports games and GTA, but they never left.
Singstar wasn't on the list (possibly due to all the SKUs), but I'm pretty sure it did a lot worse on the PS3 and franchise sales in PAL is said to be 16 million on its wiki page. I couldn't find any sales for Buzz, but I think that did decent numbers in PAL. Sucks that we can't have GfK leaks :/
Edit: The PS2 also had tons of shovel ware that I'm forgetting. Probably not as much as the Wii, but it felt like most those guys just moved over to the Wii or made PS2 ports (remember those?).