You have to factor in implied odds, too. If you have 69 and 78 on board, sure, you might be able to get paid with the 5 or the 10. Problem is, only 1 gives you nuts, the other loses to 9J. If you have, on the other hand 78 with 56 on board, your implied odds are EVEN WORSE because it is FAR EASIER to let it go to 3 in a row if the 4 falls, which gives you the nuts. Luckily for you the 9 also gives you nuts and you should be able to get something for it.
That's why TRUE implied odds on softer draws like inside straight draws are higher because you get to jam with high likelihood when it comes through, plus at least the loser (if not the whole table) will call you a donkey (which you are, let's keep it real) and play you very loose. This works out to my advantage plenty of times until my kq on king high board is called by 44 on the turn and 4 comes on the river. ::shakes head::