I don't know what you've guys read but none of the models are pre-painted to my knowledge and I play the game. I hope that didn't come of snippy but whoever told you they are pre-painted is just plain wrong.
As for the cards, they just replace codexs. You get a card with each models rules so that you don't have to waist money buying a unneccesary faction codex. This is a godsend for people like me that play mercenaries and would have had to buy multiple thick books otherwise since they update all factions a bit at a time. They don't have faction books that make one group argueably the most powerful until the next book comes out.
The cards are actually one of the things I like about this miniature game. Codexs are one of 40k's biggest hinderances. Too much money for something that is more clumsy.