It was the trilogy one last time. Including ANH. That bit of advertising you remember i guess emphasised ANH since it was the very first and most memorable film but the other advertising specifically said "the Trilogy" one last time.

I remember thinking I better get me these if they wont be available again. Lucas wasnt lying either! Can you believe its been nearly ELEVEN YEARS since the OOT was last released!?! Wow.

But i still say Lucas will release the OOT on a next-gen video system within the next five years so that he will never have to release it again (since the resolution will be close to having a 4k scan of the negative). This, i believe, is the reason why it isnt on DVD--if he did that now he would just have to do it again in a couple years since DVD resolution is already outdated.