The vinegar is sufficent to remove the sizing and/or treatments. The vinegar is actually more effective for this purpose than laundry detergent.
I know many believe it but vinegar does not set dyes on cotton fabrics . It would only work if acid type dyes are used . Acid type dyes are never used on 100 percent cotton fabrics.
The benefits you are getting is actually from the washing and drying to remove the excess dye.