I think you could get away with just sending the invites. I couldn't believe it, but alot of people I know hadn't even heard of STDs and I had to explain what they were and their purpose! Someone actually said they were a bit desperate!!lol
I personally think they are a fantastic idea, especially for destination weddings. But at the same time, they aren't essential. If I didn't have time on my hands, i'd probably skip them too.