It has nothing to do with water. I'm not washing my bottles in the dishwasher. I wash them in the sink with oxiclean. It's all about the heat of the dishwasher. The heat sanitizes the bottles.
More specifically, moist heat sanitizes the bottles. Moist heat is a more efficient microbe killer than dry heat. For example, it takes around ninety minutes to render lab glassware absolutely sterile at 350F/177C using dry heat. However, lab glassware can be rendered absolutely sterile in fifteen minutes at 250F/121C using most heat.
By the way, OxyClean, like PBW is yet another cleaner that chemically resembles unscented automatic dishwasher detergent powder.
From the OxyClean MSDS (http://www.ahprofessional.com/_downloads/msds/MSDS-1605-OxiClean%20Versatile%20Stain%20Remover.pdf
Sodium Carbonate (alkalinity booster)
Sodium Percarbonate (organic oxidizing agent)
Ethoxylated Alcohol C12 - C16 (surfactant)
Sodium Polycarboxylate (anti-redeposition agent)
Sodium Metasilicate (chelating agent)
Let's examine the list of ingredients that are in a box of unscented Cascade automatic dishwasher detergent powder (my comments are in parenthesis).
Sodium Sulfate (diluting agent)
Sodium Silicate (the umbrella name for the chemical compound known as sodium metasilicate)
Modified polyacrylate (anti-redeposition agent that belongs to the sodium polycarboxylate family)
Alcohol Alkoxylate (surfactant)
Polyethylene glycol (processing aid)
Hydrozincite (etching inhibitor)
Amine Cobalt Salt (bleach catalyst)
Protease Enzyme (this ingredient should be self-explanatory to any all-grain brewer)
Amylase Enzyme (this ingredient should be self-explanatory to any all-grain brewer)