I bet the additional friction of asking for an address means most people don't bother doing anything.
Look at how many people nowadays just send a Facebook Happy Birthday message instead of a real card. In fact, I bet there is even an autoresponder in IFTTT to help send auto birthday messages.
Who know's what is real nowadays.
If it only takes 4 clicks to send a real gift to thank someone (or wish them a Happy Christmas), then this little app might be easy enough to help more of us connect with our virtual friends