Some of my decks curl and others don't - and I treat all my decks exactly hte same, so it's nothing I'm doing.
Someone said a few months ago (I can't remember who) that when the cardboard goes into teh printing process, it's on huge rollers, and stays on them for quite a while. Anyone who's ever folded a piece of paper knows that paper has memory - once folded, even if you fold it the opposite way, it retains a fold-mark forever. This person suggested that decks that curl inwards were that-way-positioned on the roller before they were printed and cut, and decks that curl outwards were the-other-way positioned on the roller.
This makes sense, especially once I ran the idea past a scientific community who Know About Things Like This. So now I feel much better about my curled decks. They will only ever curl as much as they were curled on the roller anyway - they won't end up in tight spirals like quick-cooked squid. When I use a curled deck, I bend it gently against the curl as a whole deck, then cut it and replace so that the insides are now the outsides, and bend it against the curl again.
As a result of that, not one of my decks is in a bad way.