Is there supposed to be a difference between General Tso's and Sesame Chicken besides the seeds?
These recipes aren't very standardized. Your mileage will vary greatly from one restaurant to another. 

That said, generally these are three distinct dishes. 


Orange chicken is... Orangey. 
Sesame Chicken is typically salty with a hint of sweetness, served with sesame seeds. 
General Tsos is typically sweeter with a little more heat and served with broccoli and carrots. The sauce is usually more red in color than the brown sauce served with sesame chicken. 


I would say it is not widely accepted practice to sprinkle sesame seeds on General Tso's to create sesame chicken.