Thank You Cards

I know you're supposed to send a "Thank You" card within 2 weeks of receiving a gift and no later than 3 months after the wedding. When receiving a gift, it's straight forward what to say, but when you don't receive a gift, doesn't the whole "Thank you for celebrating with us! We loved having you on our special day." - type messages get repetitive? Like, is it okay to repeat the same wording over and over? I don't know if I can find 50+ different ways to say that same message. We aren't actually accepting physical gifts and we don't have physical items on our registry (it's a charity registry since we don't have space to store anything). I'm expecting that most people won't give anything. Also, does the bride usually end up having to write all of these? I can't see my fiance writing "Thank You" cards. He also has atrocious handwriting.... Just wondering because I'll probably be so over DIYing by the end of all this.