Why use 2:1 instead of 4:1 for flush pot odds on flop?

[Lmn55d]

I've always learned that if you flop a flush draw or straight draw, you can only need to be getting 2:1 pot odds to continue. In other words, you can use the chances that you will hit by the river instead of the chances of hitting on the next card (which would be 4:1). If my understanding is correct, you can do this because you will almost always have odds to call bets on the turn also. In No Limit, I am used to using the 4:1 figure because this is not true nearly as often. My question is basically this: When using the 2:1 figure, how do you take into account the bet/bets you will be calling on the turn?? Any info to help me understand this concept would be appreciated.

[Cooker]

The 2 to 1 rule comes into play several ways. First, you can include the likely bet that you will have to call on the turn as well (also include the bettor's bet on the turn) when calculating pot odds. For example, the pot would be current pot + his turn big bet (you may even include his big bet on the river if you hit for implied odds here) and your price to call would be the bet you must call on the flop + 1 big bet from the turn. If this gives you better than 2 to 1, call. Another choice is if you figure to have one other caller, then you are guaranteed 2 to 1 odds for all future bets, so you may once again call.

The idea is that you have decided to take the 2 to 1 shot of going all the way to the river, so you must be fairly sure that you have 2 to 1 on your current bet plus all future bets as well (and you may include some implied odds on your raise or bet on the end if you hit).

Another choice is that if you figure a raise may buy you a free card and slow down the bettor on this round, then you would only need 2 to 1 on a raise for this to be correct. This is almost always correct against a fairly timid player if you have position (and may even be correct out of position if you have check raised both the flop and turn a few times with strong hands, which I frequently do for just for some out of position free cards).

The reason why this is no good in NL is because you cannot guarantee future bet sizes, so you frequently cannot accurately estimate the bet you may need to call on the turn. However, if you or your opponent is going to be all in on the flop, you would only need 2 to 1 to call in NL, but you probably knew that.