Yahoo has an interview with someone who writes greeting cards for a living. The section on word choice is fascinating:
We tried to avoid 'soul mate terminology' because you don't know how well a couple is going to know each other or how well they're getting along. Some one might not feel comfortable using the word 'love' which is where the word 'special' comes in. You'll see that again and again on greeting cards: "for a special mom" or "for a special person." The word special can mean anything from "you're the most beautiful person to me" to "I'm glad I don't live that close to you anymore."
Getting married has been an interesting exploration of different greeting card strategies. My father's family sends whimsical, funny cards. My mother's family is apt to forego them entirely (except for my grandmother, who doesn't write notes, but does underline key words). My husband's family sends cards, often blank, with long, lovely messages in them. My husband himself is eerily skilled at finding adorable, highly specialized cards and gifts. My personal favorite: