Here's the only logic that I have ever noticed with regard to this subject. It seems that clothes washers always have a 90 degree (flat) plug, yet gas dryers always have a 180 degree (straight) plug. This permits both appliances to share the same duplex receptacle.
I haven't seen a gas dryer in nearly 30 years in these parts, in fact this "knowledge" comes from watching home improvement shows that showcase California, Chicago, New York or New Jersey homes. Electrical people keep an eye out for those things, you know.
Most clothes dryers here are electric, so I can't say that my observations on this topic are completely accurate.
