Definitely agreed that truly blue smoke (dark blue oily smoke) means that oil is in the cylinders, and yes, in that situation a leaky valve is the most common cause.

My point is that sometimes a layman, not used to seeing the difference between the two, might say "blue smoke" when what he really means is "white steam".

A puff of white steam in the morning is a leaky head gasket, not a leaky valve.