Re: It may be a US "standard", but...
So what is defined in Scotland is, in your mind, automagically correct?
That's a trifle parochial, isn't it?
Frankly, I never saw a real difference between one space, wide spaces and double spacing when reading any given document. My brain doesn't even register the whitespace, unless it is egregiously wide. Do the people you cite who supposedly find it easier to read double spaces go into a tizzy when confronted with tight and loose lines in fully justified text?