actually, drawing to a 4 flush is more like 1 in 5 than 1 in 4 - because if you hold 2 clubs, and the board holds 2, there are only 9 left, out of say, 48 on the flop). outside straight draw is 1 in 6 (8/48 on the flop).

It's true, on the flop you get 2 chances, which makes the odds of you hitting on either turn or river more like 1 in 3, but you have to call another bet on the turn if you miss.