There's no disc full of LotR merchandise ads.
The extended version will have TONS of extra goodies. The only "merchandise" advertised on the "cheap version" is the Extended Version trailer, and the preview of the Return of the King video game (and TTT game is so much fun, and heavily integrated with scenes from the films, you can't really complain about there being an ad).
Tinman, it's not that they weren't happy with the theatrical cut: they just HAD to cut stuff for time. It was nearly a 4 hour movie, and the masses of America, as well as plenty of impatient critics, probably would have complained or demanded an intermission or something. Cutting to 3 hours made it accessible for even more people, and gave them the extra time needed to finish up the extras for the extended release.
Looking at these films, at how much artistry went into them, how much work, and how it's all come together so quickly... makes me despise the Star Wars prequels all the more.