Actually, its a natural born process in a woman's brain. Its not even an issue of being raised that way, as Julliana said, though that may reinforce it. But women, by nature, speak in hints and signs, but also women are naturally better at picking up and deciphering these things. For example, bypassing any specialized learning, by nature women read body language better than men, on average. They are speaking that way because its part of their makeup and its natural. They are likely not aware they do it, and are therefore not aware that men are not getting it.
Modern psychology encourages women to be more direct towards men, especially in a marriage situation. If you want your husband to take you on a date to a fancy restaurant, don't leave a magazine open to that page and expect him to piece together this mystery. Just tell him, hey i'd love to go to Che Snobby's this weekend, just the two of us *wink wink. That way, you can actually have a chance at going, instead of sitting home watching CSI reruns and eating microwave popcorn while your husband belches his way through a few sodas in his sweats.