Xscape2041: Did you buy the standalone version of Riven or the compilation? If its the compilation with multiple Myst games, they are also based on the cd-rom versions if im not mistaken.
Veovis: I think every version of the Riven DVD is actually the "real" DVD-version. I have both the original and the Myst 10th anniversary edition DVD of Riven and I'm pretty sure they are identical apart from the newer quick time version on the newer release. The other collections of Myst games do contain the CD version, but does not come on a DVD disc.
Edit: The last time I played Riven I used a non-official build of ScummVM and the original DVD version. Worked like a charm. Hopefully it will be included as an officially supported game eventually.
I have all 3 disc versions of Riven. The file sizes on the discs seem to concur with what you said.
The CD version shows smaller file sizes, which may result in poorer Quicktime video quality, although I think the difference is negligible:
Disc 3 of the CD version shows:
j_Data1.mhk 9/15/1997 2:20pm 305,478 KB
j_Data2.mhk 9/15/1997 5:02pm 305,478 KB
The two DVD versions are identical:
1998 DVD version shows:
j_Data1.mhk 6/13/1998 2:56pm 323,410 KB
j_Data2.mhk 6/13/1998 2:57pm 339,179 KB
2003 10th Anniversary DVD also shows:
j_Data1.mhk 6/13/1998 3:56pm 323,410 KB
j_Data2.mhk 6/13/1998 3:57pm 339,179 KB