How do you feel about wedding honeymoon registries?

I received a wedding invitation and was informed that the happy couple was registered at a honeymoon registry, where I could contribute to their wedding trip to Hawaii. I’m not sure how I feel about this. On the one hand, it’s practical. On the other hand, I feel like I’m being shaken down. If we don’t pony up for the trip, does that mean they don’t go? Is this a new trend?