Both formats originally had no concept of unskippable sequences. Pressure from the studios caused revisions to the specs. I still have the little piece of paper that got sent out (That we were supposed to paste in) adding unskippable titles to my HD DVD spec.Interesting, always cool to hear backstory tales. Shame those minutes aren't public Yeah it really shows that bluray's interactivity stack was added more in haste because it's quite appaling in it's functionality. But as slow and crude as blurays menus, etc, are i think that's only one of the ways they are shooting themselves in the head ultimately. Forced trailers, etc just kill the experience.
Even without unskippables, Universal and Paramount engineered their own by catching the remote commands and ignoring them during their "unskippable" sections.
BD-J was added in return for Disney joining the BDA. BD+ was added to keep Fox happy. Unskippables was pretty much all the studios. Basically everything people hate about BD is a result of studios mucking with what was originally a very elegant format.