In terms of card size, you need to think like Scrooge McDuck. Even if it only costs $1 extra to go from a 128 MB card to a 256 MB card, that's a $1,000,000 lost if your game sells a million copies. And $1 is a random guess - it might be a lot more or a bit less.
The dollar may be worth spending if it's needed to add the features that will make the game a hit, but if the developers can squeeze it into a smaller card, you can increase your profit margin (hopefully I'm using that term correctly, because I'm NOT an accountant. :))