For me our away support is very good, and pretty much in line with our home support, i.e. usually in the top two or three in the Championship. We usually sell out pretty much every Saturday 3pm kick off.
However, there are those few clubs who just seem to sell out no matter what ridiculous time the game is scheduled. No idea if there's any substance behind it but I've always thought it must be much more convenient for the likes of Leeds fans to go away from home, as everyone you know is a Leeds fan and so you've always got someone to go with. As a young lad you've literally got double the chance of being collared in to it, double the chance of collaring a mate in to it and then double the chance of a mate to tag along with. Half my mates are Wednesdayites (probably less), but I often wonder how much better my away day life would have been if we'd all supported the same club, and it would definitely have translated in to attending more games (I've still attended about 2/3 for the last 20 odd years).