Previous to Soulstorm that figure stood at seven - representing the number of 40k races that featured after Dark Crusade, Dawn of War’s last outing.
The answer to that conundrum lies within a certain magic number. With that in mind, you have to wonder what minds were at work to conceive Soulstorm - when in almost every area the underlying gameplay has been refined (or superseded in the case of the graphics) multiple times over.