The cool thing about Myst being built in HyperCard is you can just change the file type from APPL to STAK and open it up in HyperCard and mess around. All of the color, video and audio was built with XCMDs, but the buttons and logic around the puzzles is in HyperTalk.

I think what drove them away from being HyperCard-native for Riven was the difficulty in producing a Windows version