Just like any other thing, Poker has evolved. Just look at the following citation to give you an idea of the situation.
"Back in the day when we wrote Rounders, if you'd read Super System you had an edge over 80% of the players in card rooms and 99% in home games. Now that book and books like it are the basic education that every player has, along with their PhD in math or game theory and a few million hands under their belts."
-- Screenwriters of Rounders, David Levien and Brian Koppelman