That's like comparing apples and oranges.
 
Gym Styles is a three-DVD split.
 
STS is a 41 (?) DVD system: a three-month program divided into three mesocycles, each with a different training goal. Meso 1 is for endurance. Meso 2 for hypertrophy (muscle building) and Meso 3 for strength. 
 
The similarities are that both GS and STS are three-day splits.  Also, GS is probably similar to one of the mesocycles (1 or 2 : I forget how many reps we do for most exercises in GS).