Must tomato seeds "start indoors"?

I have a package of cherry/grape tomato seeds for a big clay pot on my porch. The instructions say “Start indoors in a warm, well lighted area 6–8 weeks before planting outdoors”.

I want to simply put them in the dirt, water and wait. I’m in northern Illinois, frost is highly unlikely. The pot gets at least 6 hours of direct sun (on a sunny day).