you want to be in big multi way pots because they are the only way you're going to get pot odds. If you're heads up against AA you're going to have to flop a straight/flush if you are going to be able to profitably continue because your opponent may well be betting the ranch. Also 45 is worse than 89 because 45 is going to be the arse end of most straights you can make, if 678 comes you can't drive the betting and if a 9 or 10 comes you are just hoping no one has one. Also 45 is trying to make a wheel but as soon as the ace comes down the betting is going to be that much higher from people who have a pair of aces, 89 can make a straight with innocuous looking cards.