The thing is, every single Mario Party game has sold over a million, with 5 out of 8 selling over 2.
http://vgchartz.com/worldtotals.php?name=mario+party&console=&publisher=&sort=Total
Mario Party is a proven franchise, and 8 came out around a time where there weren't very many Wii games.
However, Sonic and Mario at the Olympics will come out during a very hot period, with several AAA games. It could easily sell over a million, but Sega will be sorely disappointed if they're hoping for 4.







