... I've used copyrighted works on visual greeting cards meant for family and friends, but that is well within the realm of legality..
Really? I think the publishing companies and record label will tell you something different. Last time I checked, wedding videos were meant for family and friends...but that's not "well within the realm of legality"?

Wrong. If you seriously wanna go toe to toe on the law in this realm, I'm exceptionally excited to do so. Bring your best game.
Making a greeting card for a wife, brother, daughter, son, father, mother....is personal use. It's one replication for a family member. It doesn't hit the internet, isn't a duplication, isn't a violation of sync, and is very well covered by several sections of the US Copyright code, and falls into similar realms of the DCMA. Additionally, Berne provides specific permissions for personal use.
Personal use does NOT cover multiple replication of a song(s) by a semi-professional video editor for weddings, events, nor even specifics like syncing music to video for sporting events under an ASCAP or BMI license. It's why you don't see that done at hockey, baseball, or similar games. They can play a video or graphic that is relevant to the music being played (and a good producer will do exactly this) but they cannot be synced in anyway.
In other words, comparing a personal greeting card for a family member that is never burned to disc, never sees the public spaces on the web, and is essentially a one-time play doesn't even remotely approach songs used on wedding videos in terms of similarity.
Douglas Spotted Eagle
Author, producer, composer
www.vasst.com
"I enjoy music, long walks at sunset on the beach, and poking dead things with a sharp stick."