This is only true because someone who did understand the more complicated principles designed the appliances in question. High voltage and high frequency are where the most common and intuitive understanding of electricity break down. Anything above about a megahertz or a few hundred volts and you will start to see relatively strange things happen.
My point is that few people work with high frequencies.
For most practical tasks, even the fact that we're working with AC rather than DC can be glossed over. People can plug in 120 V into Ohm's law and get the right result even though actual voltage fluctuates between -170 V and +170 V.
