According to a recent audio commentary on a Simpsons DVD, using even a snippet of a song can cost $10,000 to license. There was no mention as to whether that's how much a "popular" song would cost. Also, you can't entirely blame a studio for wanting to keep a cap on production costs when SO many older TV shows bomb on DVD. They're simply not going to take that chance. If they tried to license extra songs and charged a higher retail price then fans would gripe about that just as much, perhaps even more so. Mr. & Mrs. La-Z-Boy Recliner wouldn't know or care that it was because of music rights issues. They'd just know it cost more when they tried to pick it up from their local Wal-Mart with the 24 hour pharmacy.