There are some realistic sides to Spore: i.e. blood that appears near a dead creature, the Tribal age battles (none showed so far but confirmed) Tanks nuking cities (seen) and mass destruction of planets (seen).
Blood isn't so good for the common people methinks, 'cause in the GDC 2005 video the audience didn't respond positivally when the Willosaur killed the Hopper and when the UFO dropped the Spiderthing on the moon who exploded.
Also, pretty much every Maxis game had something cartoony to them (like The Sims, Simplanet and Simant) and they selled good too, people loved the games (myself included) so why should Spore be any different?