The garment has a longer life because it has the support of the underlayers. This takes a little more research, and care in construction, but the results are more durable. Finishing is everything. Besides these factors, another aspect that separates clothes from costumes is accessories. Accessorizing completes an outfit.
Hats are definitely important.
It is the small details that make a garment into clothes. I shy away from saying that I do costuming, because of the negative connotation. I always prefer to be referred to as a clothier. I make clothes for my family. We are so active that they have to be clothes.